Search found 98 matches

by Brian Tangsombatvisit 1C
Mon Feb 10, 2020 6:00 pm
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Entropy between molecules
Replies: 2
Views: 8

Re: Entropy between molecules

More complex and larger molecules have higher residual entropies, since they have more vibrational/rotational modes and possible states of arrangements. Also, all molecules in the gas phase have more residual entropy than all molecules in the liquid phase, which all have more entropy than molecules ...
by Brian Tangsombatvisit 1C
Mon Feb 10, 2020 5:58 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 4C.3b
Replies: 1
Views: 14

Re: 4C.3b

for a system at constant volume, there is no work being done since this cancels out the term. therefore, the internal energy equals heat, which is q (U=q). The equation for enthalpy is H = U + PV, so in order to find enthalpy, you would plug in q for U and nRT for PV if you are given moles and tempe...
by Brian Tangsombatvisit 1C
Mon Feb 10, 2020 3:06 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: average kinetic energy
Replies: 1
Views: 18

Re: average kinetic energy

For an ideal gas, the only type of energy that contributes to its internal energy is the average kinetic energy (since supposedly for an ideal gas there are no interactions between the molecules, so the gas's energy only comes from its motion, KE). The equation for internal energy (avg KE) of an ide...
by Brian Tangsombatvisit 1C
Mon Feb 10, 2020 3:00 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: entropy values
Replies: 1
Views: 8

Re: entropy values

the 2 main types are residual/positional/statistical and thermal entropy. Residual entropy is related to the number of microstates a system can have, which increases with greater volume or greater number of states or greater number of atoms (calculated by S = kblnW or deltaS = nrln(v2/v1)). Thermal ...
by Brian Tangsombatvisit 1C
Mon Feb 10, 2020 2:57 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Reversible vs. Irreversible reactions
Replies: 1
Views: 12

Re: Reversible vs. Irreversible reactions

Reversible work = integral of Pdv, which simplifies to -nRTln(v2/v1). External pressure is not constant. During reversible processes, the system is always at equilibrium and therefore the entropy for these systems is 0. These processes are usually isothermal, meaning that energy lost by the system t...
by Brian Tangsombatvisit 1C
Mon Feb 10, 2020 2:53 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: heat
Replies: 1
Views: 9

Re: heat

q is heat and is in units of joules. It is really heat transfer from one object to another. Heat capacity is the amount of heat needed to raise an object by 1 degree Celsius, in units of J/C. It is an extensive property since it depends on the amount of material present (larger object = larger heat ...
by Brian Tangsombatvisit 1C
Sun Feb 09, 2020 11:59 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Midterm Review #12b
Replies: 3
Views: 34

Re: Midterm Review #12b

would the enthalpies for the reactants and products in steps 1 and 3 be both positive? or would reactants be positive and products be negative?
by Brian Tangsombatvisit 1C
Sun Feb 09, 2020 11:08 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Midterm Review #12b
Replies: 3
Views: 34

Midterm Review #12b

Suppose a researcher finds that delta Hrxn = -2756 kJ for the reaction at 200. C. Assuming all heat capacities are constant, calculate delta Hrxn at the temperature of the human body, 37 C. Hint: since enthalpy is a state function, the process can be divided into three steps. Can somebody help me on...
by Brian Tangsombatvisit 1C
Mon Feb 03, 2020 10:43 am
Forum: Calculating Work of Expansion
Topic: Calculus on The Midterm
Replies: 8
Views: 28

Re: Calculus on The Midterm

Right now, the only instance where we would have to use calculus is calculating the work done by reversible expansion, which is given by w = -(integral) Pdv. However, in many cases this can simplify to w= -nRTln(V2/V1), which is a simplified version of the integral that we can use if are given the n...
by Brian Tangsombatvisit 1C
Mon Feb 03, 2020 10:38 am
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Shift Change Rules
Replies: 5
Views: 39

Re: Shift Change Rules

Some extra things to remember: when heating an endothermic reaction, the K of the reaction permanently increases; conversely when heating an exothermic reaction, the K of the rxn permanently decreases. Also, when determining reaction shifts according to changes in pressure (and the rxn involves gase...
by Brian Tangsombatvisit 1C
Mon Feb 03, 2020 10:31 am
Forum: Third Law of Thermodynamics (For a Unique Ground State (W=1): S -> 0 as T -> 0) and Calculations Using Boltzmann Equation for Entropy
Topic: Boltzmann Equation
Replies: 4
Views: 28

Re: Boltzmann Equation

To get a number for W, you would have to determine the total number of possible states that your molecule or atoms could be in. For a 2-state system, the total number of possible outcomes your system could have is 2^n, where n= the number of atoms. You would typically use this equation to solve for ...
by Brian Tangsombatvisit 1C
Mon Feb 03, 2020 10:28 am
Forum: Calculating Work of Expansion
Topic: Integral Calculations
Replies: 3
Views: 14

Re: Integral Calculations

For reversible expansion, if we know the number of moles, temperature, and final/initial volume of the sample, we can just use the simplified version of the integral, which is w = -nRTln(V2/V1) instead of integrating. If we were to integrate, I believe we would need a function for pressure with volu...
by Brian Tangsombatvisit 1C
Mon Feb 03, 2020 10:25 am
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: Formula for isothermal, reversible equilibrium
Replies: 4
Views: 29

Re: Formula for isothermal, reversible equilibrium

When using the equation -nRTln(V2/V1) for reversible reactions, does n stand for the change in moles after the reaction takes place or does it stand for the total number of moles?
by Brian Tangsombatvisit 1C
Mon Feb 03, 2020 10:22 am
Forum: Calculating Work of Expansion
Topic: Derivative
Replies: 3
Views: 19

Re: Derivative

I guess we would actually only have to integrate if we were given some sort of equation for pressure that is a function of volume, without the number of moles or temperature for the problem. Otherwise, if we know the final and initial volume, the number of moles, and temperature at which the reactio...
by Brian Tangsombatvisit 1C
Sat Feb 01, 2020 12:44 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: units for reaction enthalpy and enthalpy of formation
Replies: 3
Views: 20

units for reaction enthalpy and enthalpy of formation

I've seen kJ and kJ/mol being used interchangeably for both reaction enthalpy and enthalpy of formation, so are either units okay? Or does enthalpy of formation typically have units of kJ/mol and does reaction enthalpy typically have units of just kJ?
by Brian Tangsombatvisit 1C
Mon Jan 27, 2020 6:03 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Specific Heat and Molar Heat Capacity
Replies: 4
Views: 18

Re: Specific Heat and Molar Heat Capacity

The units of specific heat capacity and molar heat capacity can vary in terms of temperature units, but they are distinct based on whether there are grams or moles in the denominator. Joules or kilojoules can be in either numerator, and units of kelvin or celsius are also interchangeable in both. I ...
by Brian Tangsombatvisit 1C
Mon Jan 27, 2020 5:59 pm
Forum: Phase Changes & Related Calculations
Topic: heat to raise temp
Replies: 2
Views: 33

Re: heat to raise temp

There is not really a singular equation you would use to solve this part b) of this question. Once you have calculated the heat necessary to raise the temperature of water and the heat needed to raise the temperature of the entire solution, you can just divide the heat transferred to water by the to...
by Brian Tangsombatvisit 1C
Mon Jan 27, 2020 5:48 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Steam graph
Replies: 5
Views: 15

Re: Steam graph

When water in liquid form at 100 C comes into contact with skin, energy is transferred from the water to your skin since it is at a higher temperature. However, with water in vapor form at 100 C, when it comes into contact with your skin, it condenses, transforming from a vapor to a liquid, releasin...
by Brian Tangsombatvisit 1C
Mon Jan 27, 2020 5:44 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeter Specific heat
Replies: 2
Views: 8

Re: Calorimeter Specific heat

If you were doing a calorimeter experiment in a lab, then you would have to account for the heat absorbed by the calorimeter itself and the surroundings. For the purposes of this class, however, I believe you can consider this fact to be negligible when doing homework problems and calculations.
by Brian Tangsombatvisit 1C
Mon Jan 27, 2020 5:40 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Problem we did in class 1/27
Replies: 1
Views: 15

Re: Problem we did in class 1/27

My explanation would be that the resulting solution is not 100% pure water (it has salt in it), but the total volume of the products is still 100 mL; when we are finding the volume of water we are assuming that it is the total volume of the solution after the neutralization reaction. I guess Dr. Lav...
by Brian Tangsombatvisit 1C
Tue Jan 21, 2020 3:31 pm
Forum: Calculating Work of Expansion
Topic: Math skills
Replies: 2
Views: 35

Re: Math skills

I doubt we will need to use much calculus for Chem 14B, but if we do it will probably only be basic integration and nothing very complicated. If there are special integration or calculus skills that we need to use for problems I am sure Dr. Lavelle will go through it thoroughly in lecture.
by Brian Tangsombatvisit 1C
Tue Jan 21, 2020 3:28 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Acids and Bases
Replies: 7
Views: 21

Re: Acids and Bases

Acids donate their protons and are usually written as HA, where A is the rest of the molecule. Bases accept protons and usually have an OH somewhere within the molecule (an exception to this is the weak base NH3). Really long molecules with an amine group (NH2) are usually bases as the nitrogen atom...
by Brian Tangsombatvisit 1C
Tue Jan 21, 2020 3:20 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Worksheet Practice for Test 1
Replies: 3
Views: 79

Re: Worksheet Practice for Test 1

You would set up an ice table. Initial concentrations: 1 for H2, 2 for Cl2, and 0 for HCl. We don't know how much the change is, so we represent this with -x, -x, and +2x, respectively. Therefore, the expressions for the equilibrium are: H2 = 1-x, Cl2 = 2-x, and HCl = 4x^2. Write the expression for ...
by Brian Tangsombatvisit 1C
Tue Jan 21, 2020 3:16 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 6E.3b
Replies: 1
Views: 9

Re: 6E.3b

Since Ka1 is much larger than Ka2, the second dissociation reaction can be ignored. We can just focus on the first dissociation reaction, where (COOH)2 donates one of its protons to water (like any other acid), forming H3o+ and (COOH)COO-. You would set up your ICE table like normal and solve for x ...
by Brian Tangsombatvisit 1C
Tue Jan 21, 2020 1:17 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Gas Constant (R)
Replies: 3
Views: 17

Re: Gas Constant (R)

You would choose the gas constant to use based on what unit what you want to convert your concentration value into. Generally, you would use R when solving for P given the concentration using P = (n/V)RT. If you wanted your partial pressure to be in units of atmospheres, then you would use the gas c...
by Brian Tangsombatvisit 1C
Mon Jan 20, 2020 5:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: K
Replies: 5
Views: 19

Re: K

Yeah. Even if you add a lot of reactant or product, give the reaction enough time, and it will eventually settle back to equilibrium with the same ratios of product to reactant. There will be more of both product and reactant in this scenario, but the ratio of the 2 will remain the same.
by Brian Tangsombatvisit 1C
Mon Jan 20, 2020 5:17 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: "Quick Way" for predicting response to changes in volume/pressure
Replies: 3
Views: 18

Re: "Quick Way" for predicting response to changes in volume/pressure

The explicit way to determine the response to a change in volume or pressure is to calculate the new concentrations of the each reactant and product. For example, since concentration is represented by n/V, increasing V would decrease concentration. Similarly, since pressure and volume are inversely ...
by Brian Tangsombatvisit 1C
Mon Jan 13, 2020 2:47 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Textbook question 5J.5
Replies: 2
Views: 11

Re: Textbook question 5J.5

Keep in mind that this method of determining the direction of the reaction can only be used if the pressure is increased via compression. If the pressure were to be increased by the addition of inert, noble gases, then this would have no effect of the reaction. The real reason why compression forces...
by Brian Tangsombatvisit 1C
Mon Jan 13, 2020 2:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Textbook question 5.35
Replies: 2
Views: 17

Re: Textbook question 5.35

a) Set up a quick ice table. We estimate the initial concentrations to be A=27, B=C=0. The change will be: A goes from 28 to 18, B goes from 0 to 5, and C goes from 0 to 10. We can see that the differences between initial and final concentration are in multiples of 5 (A = -10, B = +5, and C = +10). ...
by Brian Tangsombatvisit 1C
Mon Jan 13, 2020 2:30 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Kp and Kc
Replies: 4
Views: 16

Re: Kp and Kc

Typically, if you are given a reaction with all reactants and products in the gas phase (and their units are given in partial pressures, not concentration) then it's assumed you're supposed to use Kp. If you do, just denote it. You could technically still calculate Kc in this scenario (where all the...
by Brian Tangsombatvisit 1C
Mon Jan 13, 2020 2:27 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: 5I.13
Replies: 3
Views: 53

Re: 5I.13

a) convert Cl2 to mol/L (for concentration) first. Then, set up your ice table (start with 0.0010 M Cl2 and 0 M Cl). You don't know how much of Cl2 was used up, so you represent the change as -x. Plug in the expressions at equilibrium into the expression for K, which is in terms of x. Use algebra to...
by Brian Tangsombatvisit 1C
Mon Jan 13, 2020 2:21 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium constant for water
Replies: 3
Views: 9

Re: Equilibrium constant for water

H2O is a solvent, and we omit all solvents from the K expression since they will be in large excess compared to the concentrations of the other aqueous reactants and products. Its concentration will not change after equilibrium is met, so it is insignificant and can be omitted from the K expression.
by Brian Tangsombatvisit 1C
Mon Jan 06, 2020 7:07 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: 5G.3
Replies: 8
Views: 58

Re: 5G.3

In this case, since all the reactants and products for both reactions are in the gas phase, it is easier to derive the Kp if given the units for the gases. This is because Kp is another way to write the equilibrium constant, but for a reaction with all gases since each reactant and product will have...
by Brian Tangsombatvisit 1C
Mon Jan 06, 2020 7:01 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Constant
Replies: 3
Views: 28

Re: Equilibrium Constant

If a molecule that is more stable than the previous molecule can form, then it will readily form this new molecule, since nature favors stability. Therefore, if a product is more stable than the reactants, as the reaction proceeds, more product will form, resulting in a higher equilibrium constant s...
by Brian Tangsombatvisit 1C
Mon Jan 06, 2020 5:34 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Equilibrium Constant
Replies: 8
Views: 60

Re: Equilibrium Constant

The equilibrium constant is written as Kc when you use the concentrations of the reactants and products in the formula, in mol/L. The equilibrium constant is written as Kp when you use the partial pressures instead of the concentrations for the equation. You cannot mix concentrations and partial pre...
by Brian Tangsombatvisit 1C
Mon Jan 06, 2020 5:31 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Writing expression for K
Replies: 5
Views: 54

Re: Writing expression for K

You can use partial pressures when all the reactants and products of a reaction are in the gas phase and when the units are in the gas phase (bar, atm, mmHg, Torr, etc). You normally use concentrations when other phases other than the gas phase are involved in the reaction, and you can use PV=nRT to...
by Brian Tangsombatvisit 1C
Mon Jan 06, 2020 5:26 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Reactant Quotient vs Equilibrium Constant
Replies: 3
Views: 35

Re: Reactant Quotient vs Equilibrium Constant

You would calculate the reactant quotient when you want to determine whether the reaction will proceed in the forward or the backward direction, assuming that the reaction is currently not at equilibrium. If the reactant quotient is greater than the equilibrium constant, then the reaction will proce...
by Brian Tangsombatvisit 1C
Sat Dec 07, 2019 10:35 pm
Forum: Naming
Topic: naming ligands in alphabetical order
Replies: 2
Views: 25

naming ligands in alphabetical order

When naming coordination compounds given their formula, just to make sure, for NC (isocyano) and NCS (isothiocyanato), when alphabetizing the ligands you would could the first letter of each of these ligands as "i," correct? So for [Fe(NC)3F3]6- it would be trifluorotriisocyanoferrate(VI)?...
by Brian Tangsombatvisit 1C
Sat Dec 07, 2019 12:18 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: pH of a solution
Replies: 2
Views: 18

pH of a solution

Lyndon sees his crush and panics, accidentally dropping 382.7 mg of HCl and 147.1 mg CaO into a 1L flask. After filling that flask with water up to the 1L mark, what is the pH of the resulting solution?
by Brian Tangsombatvisit 1C
Sat Dec 07, 2019 11:49 am
Forum: Biological Examples
Topic: heme complex chelating?
Replies: 3
Views: 57

heme complex chelating?

Is the porphyrin ligand bound to Fe, which forms a heme complex, chelating? Do we also need to know the shape of myooglobin, which is octahedral? But the shape of the heme complex is square planar..
by Brian Tangsombatvisit 1C
Fri Dec 06, 2019 11:49 pm
Forum: Bronsted Acids & Bases
Topic: TM cation acting as Lewis acids
Replies: 1
Views: 23

TM cation acting as Lewis acids

One example Dr. Lavelle did in lecture was [FeCl2(H2O)4], where the charge on iron was +3, so the charge on the overall molecule was +1. Because Fe was a highly charged, small cation, it weakened the O-H bond on one of the H2O's, releasing a proton and therefore acting as a Bronsted acid. It did thi...
by Brian Tangsombatvisit 1C
Fri Dec 06, 2019 5:27 pm
Forum: Calculating the pH of Salt Solutions
Topic: salts of weak bases/acids
Replies: 2
Views: 39

salts of weak bases/acids

Explain why salts of weak bases produce acidic solutions and salts of weak acids produce basic solutions. Also, how do we determine whether the salt produced during a titration makes the solution acidic or basic?
by Brian Tangsombatvisit 1C
Fri Dec 06, 2019 5:02 pm
Forum: Naming
Topic: naming formula for coordination compounds
Replies: 1
Views: 24

naming formula for coordination compounds

When writing the chemical formula for a coordination compound given its name, is there a particular order we write the anionic ligands or neutral ligands in if there are multiple? I know that you write the metal cation first, then anion ligands if any, then neutral ligands. For example, if there are...
by Brian Tangsombatvisit 1C
Thu Dec 05, 2019 12:08 pm
Forum: Naming
Topic: amine or ammine
Replies: 2
Views: 19

amine or ammine

When naming complex ions I've noticed that some people use amine to represent (NH3), while some use ammine. Is there a difference? Does it matter which we use? Also, I've noticed that dien and en use "amine" instead of ammine when writing out the full names of these structures: diethylenet...
by Brian Tangsombatvisit 1C
Wed Dec 04, 2019 8:17 pm
Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
Topic: help with 6B.9
Replies: 2
Views: 30

help with 6B.9

I tried using the relationships pH= -log[H3O+], [H3O+][OH-]= 1.0x10^-14, etc, but I can't seem to get the right values for filling out the table.
by Brian Tangsombatvisit 1C
Wed Dec 04, 2019 7:21 pm
Forum: Naming
Topic: "Ferrate"
Replies: 14
Views: 135

Re: "Ferrate"

when the transition metal is part of a complex ion that is negatively charged, you would name it using its latin prefix and adding -ate at the end instead of just using its regular name. I would say you should probably know a few of the common latin names besides iron like copper (which is cuprate) ...
by Brian Tangsombatvisit 1C
Wed Dec 04, 2019 7:19 pm
Forum: Acidity & Basicity Constants and The Conjugate Seesaw
Topic: 6C. 19 part C
Replies: 1
Views: 19

Re: 6C. 19 part C

In both HBrO2 and HClO2, the H+ atom is bonded to an O, not Cl and Br. If the H+ were bonded to the Cl or Br, then you would be correct in that the H-Br is a weaker bond than H-Cl, making it a stronger acid. However, this is not the case. To determine the acid that is stronger, we would have to look...
by Brian Tangsombatvisit 1C
Mon Dec 02, 2019 11:37 am
Forum: Calculating the pH of Salt Solutions
Topic: 6D.11 E
Replies: 1
Views: 24

Re: 6D.11 E

To show a chemical reaction of an acid reacting with water, the acid should donate one of its protons to water to form hydronium. However, since AlCl3 doesn't have any protons, it must first be hydrated with water. This makes sense since Al is a transition metal, and transition metals react with wat...
by Brian Tangsombatvisit 1C
Mon Dec 02, 2019 11:33 am
Forum: Properties & Structures of Inorganic & Organic Acids
Topic: Resonance Hybrid
Replies: 4
Views: 31

Re: Resonance Hybrid

If an anion from an acid after losing its H+ has resonance, then this resulting anion is more stable because the negative charge of the overall anion is delocalized. Since nature favors stability, the acid would continue to give away more of its H+ if the anion is stable compared to other acids with...
by Brian Tangsombatvisit 1C
Mon Dec 02, 2019 11:31 am
Forum: Lewis Acids & Bases
Topic: Oxoacids
Replies: 6
Views: 38

Re: Oxoacids

An oxoacid is a compound that contains hydrogen, oxygen, and at least one other element, with at least one hydrogen atom bond to oxygen that can dissociate to produce the H⁺ cation and the anion of the acid. Oxoacids are stronger if they have more oxygen atoms, have very electronegative anions, or h...
by Brian Tangsombatvisit 1C
Mon Dec 02, 2019 11:28 am
Forum: Bronsted Acids & Bases
Topic: Acid strength
Replies: 2
Views: 19

Re: Acid strength

For HI, Iodine is a much larger and less electronegative atom than Fluorine, so it exerts a much weaker pull on H+. As a result, HI has a weaker bond, allowing it to dissociate to a much greater extent than HF. Since the strength of an acid is directly proportional to how much it is able to dissocia...
by Brian Tangsombatvisit 1C
Mon Dec 02, 2019 11:20 am
Forum: Lewis Acids & Bases
Topic: 6D.11
Replies: 1
Views: 24

Re: 6D.11

Since Al and Cu are both transition metals, when AlCl3 and Cu(NO3)2 react with water, they become hydrated and form coordination compounds or complex ions. Al and Cu in particular like to form octahedral complexes and bind to 6 water molecules. They are both aqueous since they are dissolved in water.
by Brian Tangsombatvisit 1C
Mon Nov 25, 2019 8:57 am
Forum: Biological Examples
Topic: TM switching between oxidation states
Replies: 1
Views: 30

Re: TM switching between oxidation states

Transition metals can have multiple oxidation states because of their many electrons in the d subshell. The transition metals have several electrons in this shell with similar energies, so different numbers of them can be oxidized, depending the circumstances, resulting in different oxidation states...
by Brian Tangsombatvisit 1C
Mon Nov 25, 2019 8:53 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Molecular shape and central atom
Replies: 3
Views: 41

Re: Molecular shape and central atom

The atoms in Group 12 are transition metals, so they would likely either form ionic compounds with nonmetals or coordination compounds with ligands. There is no real way to determine a molecule's shape just looking at the central atom. You would have to determine which molecule you want to look at f...
by Brian Tangsombatvisit 1C
Mon Nov 25, 2019 8:50 am
Forum: Biological Examples
Topic: biological application
Replies: 2
Views: 45

Re: biological application

Dr. Lavelle mentioned many examples of biological applications in lecture, but I wouldn't say any one of them is more important than the other. Some examples he talked about was Cisplatin (cis-diamine-dichloro-platinum(II), a chemo drug which forms a coordination compound w/ DNA to stop cell divisio...
by Brian Tangsombatvisit 1C
Mon Nov 25, 2019 8:42 am
Forum: Ionic & Covalent Bonds
Topic: ligands
Replies: 5
Views: 69

Re: ligands

A ligand is an ion or molecule that binds to a central metal atom to form a coordination complex, and the nature of the bonding with the metal ion can range from covalent to ionic. Ligands can be neutral or anions. Some examples of neutral ligands are H20, NH3, NO, and CO. Some anion ligands are any...
by Brian Tangsombatvisit 1C
Mon Nov 25, 2019 8:38 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Bond Angle of Single Electron of A Free Radical
Replies: 3
Views: 34

Re: Bond Angle of Single Electron of A Free Radical

I would think that since a radical is only 1 electron, it would cause less repulsion than a lone pair since it has 2. Therefore, I would conclude that a radical results in larger bond angles than if it was a lone pair because it repulses the other bonds less.
by Brian Tangsombatvisit 1C
Mon Nov 18, 2019 8:53 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Trigonal Bipyramidal
Replies: 5
Views: 37

Re: Trigonal Bipyramidal

Yep, electron arrangement is only determined using the # of regions of electron density, while the molecule's shape is determined using the actual number of lone pairs and bond pairs. This means that molecules with different shapes (and different formulas, ex: AX4E for SF4) can have the same electro...
by Brian Tangsombatvisit 1C
Mon Nov 18, 2019 8:50 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Pi bond
Replies: 4
Views: 27

Re: Pi bond

Yes, if you tried to rotate a molecule along its double bond, the pi bond would break. This would only occur during a chemical reaction. You can only rotate molecules along their sigma bonds since doing this would not break the bond.
by Brian Tangsombatvisit 1C
Mon Nov 18, 2019 8:48 pm
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Intermolecular Forces in CO2
Replies: 4
Views: 24

Re: Intermolecular Forces in CO2

CO2 only has London dispersion forces, or induced dipole - induced dipole interactions. Even though CO2 has polar bonds, the molecule is nonpolar because the dipoole moments cancel out. A nonpolar molecule cannot have dipole-dipole interactions. Only polar molecules can.
by Brian Tangsombatvisit 1C
Mon Nov 18, 2019 8:43 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Lone Pairs
Replies: 3
Views: 27

Re: Lone Pairs

Lone pairs have a stronger repulsion than bonding pairs because bonding pairs are farther away from the central atom since it needs to be connected to the sharing atom. Also, lone pairs are delocalized, meaning they are more spread out than bonding pairs and therefore fill more volume. They are also...
by Brian Tangsombatvisit 1C
Mon Nov 18, 2019 8:40 pm
Forum: Hybridization
Topic: quickest way to find hybridization
Replies: 1
Views: 19

Re: quickest way to find hybridization

The easiest way is to find the # of regions of electron density first by drawing the correct Lewis structure. Once you have found this number, you can determine the number of hybrid orbitals. Make sure the total number of orbitals and electrons remain the same before and after hybridization and that...
by Brian Tangsombatvisit 1C
Wed Nov 13, 2019 11:30 am
Forum: Determining Molecular Shape (VSEPR)
Topic: Single/Double Bonds in Resonance
Replies: 6
Views: 42

Re: Single/Double Bonds in Resonance

All of the different Lewis structures contribute to the resonance model since it is a blend of these structures. Because of this, all of the bond lengths in this type of atom are the same, but are in between a single and double bond's length. However, resonance does not affect a molecule's bond angl...
by Brian Tangsombatvisit 1C
Wed Nov 13, 2019 11:22 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: intermolecular forces
Replies: 8
Views: 53

Re: intermolecular forces

There are only dipole - dipole interactions when the overall molecule has a dipole. This is the case for a) and c) since the dipoles within the molecule do not cancel each other out and result in an overall dipole moment for the entire molecule. However, for d), even though the s-o bond is polar, th...
by Brian Tangsombatvisit 1C
Wed Nov 13, 2019 11:19 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Covalent bonding
Replies: 5
Views: 30

Re: Covalent bonding

Intermolecular forces occur between two molecules, not between two atoms. Examples of intermolecular forces include induced dipole - induced dipole (LDFs), induced dipole - dipole, dipole - dipole, ion - dipole, and ion - ion (in order of increasing strength). Induced dipole - induced dipole forces ...
by Brian Tangsombatvisit 1C
Wed Nov 13, 2019 11:16 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: Intermolecular forces
Replies: 1
Views: 20

Re: Intermolecular forces

Van der waals is just another way of saying London forces, which are also known as induced dipole - induced dipole forces. All molecules have these forces, whether they are polar or not. When two molecules get close to each other, their electron distributions fluctuate, resulting in induced dipoles ...
by Brian Tangsombatvisit 1C
Wed Nov 13, 2019 11:12 am
Forum: Interionic and Intermolecular Forces (Ion-Ion, Ion-Dipole, Dipole-Dipole, Dipole-Induced Dipole, Dispersion/Induced Dipole-Induced Dipole/London Forces, Hydrogen Bonding)
Topic: hydrogen bonding
Replies: 3
Views: 13

Re: hydrogen bonding

You should also remember that hydrogen bonding is the actually the intermolecular attraction between the hydrogen atom covalently bonded to O, N, of F and another O, N, or F with an available lone pair.
by Brian Tangsombatvisit 1C
Mon Nov 04, 2019 4:53 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Highly Polarized
Replies: 2
Views: 23

Re: Highly Polarized

Highly distorted electrons (from a large anion with weaker pull, for example) are described as being highly polarizable, which results in an ionic bond with more covalent character. Ions which cause large distortions have high polarizing power (cation). Anions usually have strong pulls, while cation...
by Brian Tangsombatvisit 1C
Mon Nov 04, 2019 4:44 pm
Forum: Lewis Structures
Topic: 2B.1b
Replies: 3
Views: 26

Re: 2B.1b

The structure that you have drawn has formal charges of 0 on the Cl and O, however the C has a formal charge of +2 since it only has 2 bonds. It also shows 26 valence electrons instead of 24. In order for the formal charges on all the elements to be 0, Carbon must be placed in the middle and have a ...
by Brian Tangsombatvisit 1C
Mon Nov 04, 2019 4:40 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Large Anion + Small Cation
Replies: 2
Views: 38

Re: Large Anion + Small Cation

The ionic bond behaves more covalent when you have a large anion and small cation, since the anion has a lower electronegativity and the cation has a higher electronegativity. This results in covalent-like behaviors since the cation and anion are more likely to share the electrons between them, rath...
by Brian Tangsombatvisit 1C
Mon Nov 04, 2019 4:37 pm
Forum: Formal Charge and Oxidation Numbers
Topic: Formal Charge
Replies: 9
Views: 67

Re: Formal Charge

To determine the most stable Lewis structure, you would see which one has the most formal charges that are closest to 0. Molecules that have a net positive or net negative charge will inevitably have one or two elements that do not have a formal charge of 0, since a molecule's formal charges are sup...
by Brian Tangsombatvisit 1C
Mon Nov 04, 2019 4:33 pm
Forum: Administrative Questions and Class Announcements
Topic: Midterm Electron Configuration
Replies: 5
Views: 47

Re: Midterm Electron Configuration

Professor Lavelle said in lecture previously that we would not be focusing on elements including the f-block. However, we did do that example in lecture today with an element that included the f-block. For studying, I would focus on elements including the d-block, but know how to do an electron conf...
by Brian Tangsombatvisit 1C
Mon Oct 28, 2019 10:01 pm
Forum: Trends in The Periodic Table
Topic: Effective nuclear charge
Replies: 3
Views: 38

Re: Effective nuclear charge

I'm not sure how to exactly calculate the effective nuclear charge felt by an electron when there's electron shielding. Professor Lavelle said in lecture that the outer electrons feel a reduced electrostatic attraction to the nucleus, resulting in an effective nuclear charge. It's not quite clear ho...
by Brian Tangsombatvisit 1C
Mon Oct 28, 2019 9:57 pm
Forum: Ionic & Covalent Bonds
Topic: How to count valence electrons with the d block
Replies: 4
Views: 27

Re: How to count valence electrons with the d block

The 3d shell is a continuation of the n=3 shell, so it does not play any role in affecting the number of valence electrons. The number of valence electrons is determined by the number of electrons in the outermost shell. The outermost shell for period 4 elements is the n=4 shell, therefore these tra...
by Brian Tangsombatvisit 1C
Mon Oct 28, 2019 9:54 pm
Forum: Ionic & Covalent Bonds
Topic: 2A23 Part E
Replies: 2
Views: 33

Re: 2A23 Part E

Bismuth is one of the weird elements that doesn't always follow the typical rules or have the usual characteristics of one of the first 18 atoms. When you see the roman numeral "III" just know that it is a cation with a charge of +3. I don't think we would have to memorize this cation of B...
by Brian Tangsombatvisit 1C
Mon Oct 28, 2019 9:50 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Rydberg formula
Replies: 2
Views: 36

Re: Rydberg formula

The En=hR/n^2 formula represents the energy an electron has when it is in the nth shell. The Rydberg equation, 1/wavelength=Rh((1/n1^2)-(1/n2^2), is derived from the change in energy formula, which is final energy - initial energy, meaning that it is delta E = Ef=hR/n^2 - Ei=hR/n^2. To get the Rydbe...
by Brian Tangsombatvisit 1C
Mon Oct 28, 2019 11:21 am
Forum: Lewis Structures
Topic: Multiple Elements in a Molecule
Replies: 1
Views: 15

Re: Multiple Elements in a Molecule

Usually the atom with the lowest ionization energy or lowest electronegativity goes in the center of the atom. This is because this atom is less likely to hold onto its valence electrons tightly and more likely to share its electrons with other atoms. In the case with ONF, Nitrogen should go in the ...
by Brian Tangsombatvisit 1C
Mon Oct 21, 2019 3:03 pm
Forum: *Shrodinger Equation
Topic: Calculating the probability of finding an electron at a certain location
Replies: 5
Views: 79

Re: Calculating the probability of finding an electron at a certain location

If you use Heisenberg's Indeterminacy Equation, you will find that the change in position and change in momentum variables are inversely related. Meaning, if you design your experiment so that you minimize the error found in its position, you will have a large error in momentum (velocity since mass ...
by Brian Tangsombatvisit 1C
Mon Oct 21, 2019 2:51 pm
Forum: Properties of Electrons
Topic: Problem 1E.5
Replies: 3
Views: 39

Re: Problem 1E.5

You basically have to know that different orbitals within the same shell are different distances away from the nucleus; they are not all equidistant. Therefore, they provide varying levels of electron shielding / penetrance of the nucleus depending on how far away or close they are. The s-orbitals a...
by Brian Tangsombatvisit 1C
Mon Oct 21, 2019 2:48 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: orbitals
Replies: 5
Views: 41

Re: orbitals

I believe we don't have to draw the orbitals at all for this class. For the planes, I would say just know that the s-orbital is the only orbital without any nodal planes since it has a symmetric electron p distribution. All of the other orbitals have nodal planes (areas with 0 probability of electro...
by Brian Tangsombatvisit 1C
Mon Oct 21, 2019 2:42 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: Nodal Plane Significance
Replies: 2
Views: 23

Re: Nodal Plane Significance

First of all, I would say know what nodal planes are (zero probability of electron density found here). Also, you should probably know that s-orbitals have no nodal planes and that the rest of the orbitals do have nodal planes. The s-orbital is the only orbital not to have a nodal plane since it has...
by Brian Tangsombatvisit 1C
Mon Oct 21, 2019 2:40 pm
Forum: Trends in The Periodic Table
Topic: 1st and 2nd Ionization
Replies: 5
Views: 44

Re: 1st and 2nd Ionization

When an atom has more electrons in its outer shell, its radius is bigger. This is because of electron-electron repulsion. Therefore, when you take the first electron out, the atom becomes smaller since there are less electrons. Because the atom is now smaller, the atom requires a greater ionization ...
by Brian Tangsombatvisit 1C
Mon Oct 14, 2019 11:39 am
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: 1A.11 What is common to each series that groups their spectral lines together?
Replies: 2
Views: 17

Re: 1A.11 What is common to each series that groups their spectral lines together?

Also, the Lyman series corresponds to light in the UV region, Balmer series corresponds to light in the visible region, and the lines for n=3 correspond to light in the infrared region (Paschen series).
by Brian Tangsombatvisit 1C
Mon Oct 14, 2019 11:33 am
Forum: Einstein Equation
Topic: Energy Emitted
Replies: 2
Views: 44

Re: Energy Emitted

a) from c=v(wavelength) and E=hv, derive the equation E = (hc)/wavelength. use this equation to solve for the energy, which comes out to 3.37 x 10^-19 J. b) here convert grams of Na to moles of Na by dividing by the molar mass, then multiply by Avogadro's number to find the number of atoms in the gi...
by Brian Tangsombatvisit 1C
Mon Oct 14, 2019 11:28 am
Forum: Properties of Electrons
Topic: 1E9
Replies: 1
Views: 19

Re: 1E9

n specifies shells. l specifies subshells: 0=s, 1=p, 2=d, 3=f. ml specifies orbitals of subshells (l, l-1 . . . -l), and ms specifies spin state (+1/2 for spin up, -1/2 for spin down). a) valid bc within n=4, there is a subshell d (from l=2), and -1 is a valid orbital given l=2. +1/2 is also a valid...
by Brian Tangsombatvisit 1C
Mon Oct 14, 2019 11:20 am
Forum: Properties of Electrons
Topic: 1D.1
Replies: 2
Views: 21

Re: 1D.1

The transition from the 1s orbital to the 2p orbital is making a jump from the n=1 to n=2 shell. Remember when you fill in electrons for an atom using spin up/spin down, you fill in orbitals based on their order- 1s first, then 2s, then 2p (which has 3 orbitals). The electron actually jumps from the...
by Brian Tangsombatvisit 1C
Mon Oct 14, 2019 11:13 am
Forum: Properties of Electrons
Topic: 1F.5 Question
Replies: 2
Views: 25

Re: 1F.5 Question

If an atom has a bigger radius (more shells) then it has a lower ionization energy than another atom with a smaller radius. If 2 atoms are in the same period/row, the atom with more protons has a higher ionization energy because the nucleus exerts a stronger pull on its electrons, which makes them h...
by Brian Tangsombatvisit 1C
Mon Oct 07, 2019 11:55 am
Forum: SI Units, Unit Conversions
Topic: Fundamentals: E3
Replies: 2
Views: 44

Re: Fundamentals: E3

You could determine the mass of each individual atom (for both gallium and astatine) by dividing the molar masses by Avogadro's number. Add up the mass of the 9 Ga atoms on the left, then divide this number by the mass of an individual astatine atom to find out how many astatine atoms equal the weig...
by Brian Tangsombatvisit 1C
Mon Oct 07, 2019 11:49 am
Forum: Properties of Light
Topic: Spectroscopy
Replies: 2
Views: 26

Re: Spectroscopy

Atoms and molecules have their own unique spectral fingerprint that distinguishes them from other atoms and molecules. Therefore, chemists can use spectroscopy to identify atoms and molecules within a particular object. For example, chemists are able to determine functional groups within molecules.
by Brian Tangsombatvisit 1C
Mon Oct 07, 2019 11:45 am
Forum: Molarity, Solutions, Dilutions
Topic: G 11
Replies: 2
Views: 45

Re: G 11

An alternative way to represent your answer with three significant figures is to write your answer as 1.62 x 10^-2 L. When you write your answer in scientific notation, the number before the power of 10 holds all the significant figures.
by Brian Tangsombatvisit 1C
Mon Oct 07, 2019 11:42 am
Forum: Molarity, Solutions, Dilutions
Topic: G 25
Replies: 7
Views: 112

Re: G 25

Once you see the 90 doublings of volume, you can probably assume that you don't have to do every single calculation and obtain the exact number of solute left in the solution. You can just approach the question conceptually and assume that there is basically zero solute left at the end of the proble...
by Brian Tangsombatvisit 1C
Mon Oct 07, 2019 11:38 am
Forum: SI Units, Unit Conversions
Topic: Intensive Properties
Replies: 3
Views: 30

Re: Intensive Properties

The density of a gas remains the same even if the amount of gas changes.

Density is mass/volume. If you take some amount of gas away, you decrease the mass and volume of the gas by such an amount so that if you divide the new mass and volume, you get the same density.
by Brian Tangsombatvisit 1C
Wed Oct 02, 2019 3:26 pm
Forum: Properties of Light
Topic: Amplitude? [ENDORSED]
Replies: 8
Views: 91

Re: Amplitude? [ENDORSED]

Amplitude measures the height of the crest of the wave from the midline. It's a measurement of length, so its unit is meters. Waves with tall crests have large amplitudes.
Don't confuse amplitude with wavelength, which is the distance from one crest to another.
by Brian Tangsombatvisit 1C
Wed Oct 02, 2019 3:22 pm
Forum: Molarity, Solutions, Dilutions
Topic: Calculating molarity
Replies: 2
Views: 21

Re: Calculating molarity

Yeah this would work because mmol/ml is the same formula as mol/L, but reduced by 1000. If you multiply your formula of M = mmol/ml by 1000/1000 you get the formula in correct SI units, which is M = mol/L. If you convert from mmol to mol and ml to L and plug in the numbers you will still get the sam...
by Brian Tangsombatvisit 1C
Wed Oct 02, 2019 3:11 pm
Forum: Molarity, Solutions, Dilutions
Topic: Molar Mass
Replies: 5
Views: 56

Re: Molar Mass

An ion is the same thing as the regular atom, but with a different charge. This means that the regular atom gains or loses a number of electrons, which doesn't really affect the atom's molar mass since electrons are so light. In short, ions have basically the same molar mass as the original atom.
by Brian Tangsombatvisit 1C
Wed Oct 02, 2019 3:08 pm
Forum: Molarity, Solutions, Dilutions
Topic: G 25
Replies: 7
Views: 81

Re: G 25

I think once you see an absurd number that is above 50+, you can assume that you don't have to do all the math and just approach the question conceptually. If you use the concept of limits from algebra, if a number keeps getting smaller and smaller, you can safely make the assumption that it approac...
by Brian Tangsombatvisit 1C
Wed Oct 02, 2019 2:55 pm
Forum: Empirical & Molecular Formulas
Topic: Writing Molecular Formulas with charges [ENDORSED]
Replies: 4
Views: 71

Re: Writing Molecular Formulas with charges [ENDORSED]

When you have to name ionic compounds with transition metals in them, you have to indicate the charge of the transition metal using Roman numerals in parentheses after the name of the transition metal. This is because some transition metals can have varying charges, depending on the charge of the no...

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