## Search found 56 matches

Mon Mar 11, 2019 10:00 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pre-Equilibrium Steps
Replies: 2
Views: 92

### Re: Pre-Equilibrium Steps

Usually, the problem will tell us which steps are fast and which step is slow. Then with that information, we can solve for the overall rate law.
Mon Mar 11, 2019 9:59 pm
Forum: First Order Reactions
Topic: Homework, 6th edition, 15.27
Replies: 2
Views: 99

### Re: Homework, 6th edition, 15.27

What I did was use the half-life in order to find the k value (t1/2= ln2/k). Then I would just use the integrated rate law to solve for the time required for the other scenarios. For example, when it asks for 15% of the initial concentration, you would plug in 0.15A0 into [A] and then solve. Althoug...
Mon Mar 11, 2019 9:56 pm
Forum: General Rate Laws
Topic: Homogeneous vs Heterogeneous Reactions
Replies: 1
Views: 58

### Re: Homogeneous vs Heterogeneous Reactions

Homogenous reactions are when all the products and reactants are in the same phase. Heterogeneous reactions are when the products and reactants are not all the same phase.
Fri Mar 08, 2019 2:23 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Unique Rates
Replies: 3
Views: 188

### Re: Unique Rates

Since the rates of formation/consumption for reactants and products are different due to their stoichiometric coefficients, the unique rate takes the stoichiometric coefficients into consideration to give us a rate that works overall rather than for a specific reactant or product.
Fri Mar 08, 2019 2:15 pm
Forum: General Rate Laws
Topic: Rate Laws
Replies: 8
Views: 229

### Re: Rate Laws

You might want to have a basic understanding of how the equations are derived. You mainly just need to know that you set the rate law in the form k[A]^n equal to the rate law in the form -d[A]/dt and solve.
Fri Mar 08, 2019 1:57 pm
Forum: First Order Reactions
Topic: Order reactions
Replies: 4
Views: 184

### Re: Order reactions

Usually, some sort of experimental data will be given to us so that we can figure out what order the reactants are.
Fri Mar 01, 2019 2:32 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Finding n
Replies: 12
Views: 394

### Re: Finding n

When finding n, you would want to solve for both the oxidation and the reduction half reactions. Once you get there, see how many moles of electrons are transferred in the completely balanced redox reaction; this number of moles is the number you want to use for n.
Fri Mar 01, 2019 2:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Entropy based on shape of molecule
Replies: 3
Views: 146

### Re: Entropy based on shape of molecule

In general, the more complex the molecule is, the higher the entropy because it can be rearranged in many different positions.
Fri Mar 01, 2019 2:25 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Potentials and Likeliness to be reduced/oxidized
Replies: 3
Views: 128

### Re: Potentials and Likeliness to be reduced/oxidized

Standard cell potentials give us information on how badly a compound wants to be reduced. The more positive the cell potential of the reduction reaction, the more the compound will serve as the oxidizing agent (reduction reaction). The more negative the cell potential of the reduction reaction, the ...
Fri Feb 22, 2019 1:42 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electron Transfer and Galvanic Cells
Replies: 2
Views: 82

### Re: Electron Transfer and Galvanic Cells

For a Galvanic cell, reduction occurs at the cathode, meaning the substance is gaining electrons. At an anode, oxidation is occurring, and the substance is losing electrons. These two reactions, oxidation and reduction, are paired through the Galvanic cell, meaning that the electrons lost from the a...
Fri Feb 22, 2019 1:36 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Phase changes and Entropy
Replies: 4
Views: 323

### Re: Phase changes and Entropy

Entropy always increases as a substance goes from solid to liquid to gas because as the intermolecular forces break, the molecules can move around and occupy more positions. Gas will have more entropy than a liquid.
Fri Feb 22, 2019 1:33 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Change in Gibbs Free Energy
Replies: 3
Views: 223

### Re: Change in Gibbs Free Energy

The degree symbol indicates that the reaction is occurring under standard conditions (usually 25 degrees Celsius, 1 bar pressure, etc.).
Wed Feb 13, 2019 11:24 am
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: R constants
Replies: 21
Views: 726

### Re: R constants

Whenever using the ideal gas equation (pv=rnt) we want to use the R constant with units of L*atm*mol^-1*K^-1 because the units will cancel. When solving for work or entropy, we usually use the one that 8.314 J/mol*K because the units cancel out and leave us with J. In order to be absolutely sure, ju...
Wed Feb 13, 2019 11:20 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: 3
Views: 421

### Re: Boltzmann Equation

We usually use Boltzmann's equation when a problem gives us a number of molecules and the number of positions each molecule can possess. This is because, given this information, we can find degeneracy (W).
Wed Feb 13, 2019 11:17 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Change in Internal Energy
Replies: 3
Views: 170

### Re: Change in Internal Energy

When a system is isothermal, the change in internal energy is zero.
Tue Feb 05, 2019 5:02 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: U clarifications
Replies: 3
Views: 160

### Re: U clarifications

Hey Kirsty! When the change in pressure is 0, both q and w should be considered when calculating the change in internal energy of the system. However, when the change in volume is 0, we can only focus on q. Remember that the calculation for work is dependent upon the change in volume times the exter...
Tue Feb 05, 2019 4:56 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: heat capacity
Replies: 2
Views: 111

### Re: heat capacity

Heat capacity is the amount of energy (in the form of heat) required to raise the temperature of a specific substance one degree C. e.g. the amount of energy required to raise the temperature of a sample of water is 4.184 J*g^-1*C^-1. The enthalpy of vaporization is the amount of energy (in the form...
Tue Feb 05, 2019 3:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 6th ed 103 units
Replies: 1
Views: 68

### 6th ed 103 units

The following is problem 103 from the 6th edition textbook: Calculate the molar kinetic energy (in joules per mole) of Kr(g) at (a) 55.85 C and (b) 54.85 C. (c) The difference between the answers to parts (a) and (b) is the energy per mole that it takes to raise the temperature of Kr(g) by 1.00 C. T...
Fri Feb 01, 2019 7:45 pm
Forum: Calculating Work of Expansion
Topic: formula for work with integral
Replies: 3
Views: 125

### Re: formula for work with integral

I assume this formula would be used while the pressure and the volume are both changing at the same time. In this scenario, the pressure is no longer constant and the area underneath the pressure-volume curve wouldn't be a simple box. For complex functions modeling changes in pressure, calculus is r...
Fri Feb 01, 2019 7:42 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: Analogy of Boulder
Replies: 5
Views: 259

### Re: Analogy of Boulder

Some reactions, usually exothermic reactions, occur spontaneously and are favored. There is no work forcing the reaction to occur and not heat is put into the system. Instead, the system will react on its own, releasing energy as heat. This is similar to a boulder rolling down a hill. Gravity does a...
Fri Feb 01, 2019 7:38 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Cvm and Cpm ?
Replies: 2
Views: 1308

### Re: Cvm and Cpm ?

Cv is used when the reaction is being conducted at constant volume and Cp is used when the reaction is being conducted with constant pressure.
Fri Jan 25, 2019 1:49 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Autoprotolysis
Replies: 3
Views: 192

### Re: Autoprotolysis

If a weak acid deprotonates and releases less than 10^-7 M of hydronium, then you would consider autoprotolysis. This is because if you ignore autolysis and calculate pH of an acid that creates 10^-9 M hydronium, then the pH would be basic. This would not make sense since there is an acid in the sol...
Fri Jan 25, 2019 1:45 pm
Forum: Non-Equilibrium Conditions & The Reaction Quotient
Topic: Ka
Replies: 6
Views: 221

### Re: Ka

H2SO4 is a polyprotic acid. When it loses the first hydrogen, the reaction is strong since it completely dissociates into HSO4- and H+. The second dissociation isn't so complete; HSO4- is a weak acid and has a Ka value.
Sat Jan 19, 2019 5:01 pm
Forum: Student Social/Study Group
Topic: ICE Table
Replies: 6
Views: 160

### Re: ICE Table

Ice tables usually come up when we are asked to find the concentrations of products and reactants at equilibrium, but the problem only gives us the initial conditions.
Sat Jan 19, 2019 4:50 pm
Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
Topic: Partial Pressure and Moles
Replies: 3
Views: 182

### Re: Partial Pressure and Moles

When there is a change in pressure, the volume of the system is usually changing; the amount of matter in the reaction vessel remains the same, but the amount of space (volume) that the matter takes up is partially related to the pressure being placed upon the matter. It is important to notice that ...
Sat Jan 19, 2019 4:45 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Water in K
Replies: 3
Views: 172

### Re: Water in K

When dealing with aqueous solutions with water as the solvent, we would not include water in the equilibrium constant because it is in excess. However, some equilibrium reactions include water in a gaseous phase. In this case, water would be included when solving for K.
Sat Jan 12, 2019 6:47 pm
Forum: Ideal Gases
Topic: R and T
Replies: 3
Views: 148

### Re: R and T

R is a constant and I believe it will be given to us for tests (???). T represents temperature in Kelvin. In order for us to use the ideal gas law to convert between pressures and concentrations, we will usually be given the temperature in the problem. It may also be handy to remember the conversion...
Sat Jan 12, 2019 6:40 pm
Forum: Ideal Gases
Topic: Concentration or Partial Pressure
Replies: 13
Views: 325

### Re: Concentration or Partial Pressure

I am pretty sure that the problem will specify whether we need to calculate kc or kp. It should be made explicit for us.
Sat Jan 12, 2019 6:39 pm
Forum: Equilibrium Constants & Calculating Concentrations
Topic: Intermediate Values of K
Replies: 1
Views: 110

### Re: Intermediate Values of K

I assume intermediate values are comparable to reactions with a k value of 1. When k is close to one, such as the intermediate values, the ratio of products to reactants is nearly identical. This would imply that the reaction doesn't favor either the forward reaction or the reverse reaction.
Tue Dec 04, 2018 10:09 pm
Forum: Naming
Topic: Transition Metal
Replies: 4
Views: 185

### Re: Transition Metal

I am pretty sure that for the purposes of this course we will only be working with coordination complexes with one TM. Usually, these transition metals have a positive oxidation state, therefore they will only form coordinate covalent bonds with molecules and/or atoms that have negative dipoles or n...
Mon Dec 03, 2018 4:37 pm
Forum: Identifying Acidic & Basic Salts
Topic: Salts cause acidity
Replies: 3
Views: 170

### Re: Salts cause acidity

If one of the ions in the salt is also an acid, then when the salt is added to water, the acidic ion will also react with the water. NaCl doesn't do this because neither Na+ or Cl- are acidic. Professor Lavelle used the example NH4Cl in class to demonstrate this to us because the NH4+ ion is acidic ...
Mon Dec 03, 2018 4:35 pm
Forum: Naming
Topic: Latin Names
Replies: 5
Views: 227

### Re: Latin Names

Latin names are used when the element symbol is derived from its Latin name and the overall coordination sphere has a negative charge. Some examples would be ferrate for iron (Fe), cuprate for copper (Cu), plumbate for lead(Pb), argentate for silver(Ag), aurate for gold (Au), and stannate for tin (S...
Wed Nov 28, 2018 8:07 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: So does the dipole moment point to the partial positive charge or the partial negative charge?
Replies: 2
Views: 163

### Re: So does the dipole moment point to the partial positive charge or the partial negative charge?

It depends on the model being used. The original model points towards the partial negative charge with a plus at the end by the partial negative. The modern model just points towards the partial positive charge. Howeverm I'm not entirely sure which convention is more proper for this course.
Wed Nov 28, 2018 7:47 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: Square Pyramidal
Replies: 2
Views: 148

### Re: Square Pyramidal

Square pyramidal shapes are the results of a octahedral electron arangement with one lone pair. The lone pair takes the place of one of the polar atoms. The resulting shape is the central atom with one polar atom and 4 equatorial atoms in a square pyramidal shape.
Wed Nov 28, 2018 7:45 pm
Forum: Bronsted Acids & Bases
Topic: Bronsted vs Lewis
Replies: 2
Views: 109

### Bronsted vs Lewis

Is one definition preferred over the other? Or are the two definitions equally interchangeable?
Fri Nov 16, 2018 7:15 pm
Forum: Lewis Structures
Topic: Expanded Octet
Replies: 8
Views: 368

### Re: Expanded Octet

As we learned the wave function numbers and their meaning we learned that we are dealing with a d orbital when l=2. For l to equal 2 the value of n must be at least 3. This means elements in the 3rd period possess a d sub-shell. However, we also learned that the electron configuration for an element...
Fri Nov 16, 2018 6:45 pm
Forum: Dipole Moments
Topic: Difference between dipole and london forces?
Replies: 5
Views: 214

### Re: Difference between dipole and london forces?

Dipole forces occur as a result of uneven electron sharing between two bonded atoms. For example in water, the oxygen pulls the electrons closer to it than the hydrogen atoms do. London forces occur between atoms without dipole moments. When in a proximity of one another, atoms without dipole moment...
Fri Nov 16, 2018 6:43 pm
Forum: Determining Molecular Shape (VSEPR)
Topic: AX3E2 Shape
Replies: 6
Views: 376

### AX3E2 Shape

What is the official name of a molecule with 3 ligands and 2 lone pairs around the central atom?
Thu Nov 08, 2018 5:18 pm
Forum: Polarisability of Anions, The Polarizing Power of Cations
Topic: Polarizability
Replies: 2
Views: 146

### Re: Polarizability

A good analogy for me to understand polarizability is to compare it to malleability. Polarizability, from my understanding, is how likely an atom or molecule's electron cloud will shift in response to another electromagnetic force. Malleability is a substance's ability to change form and mold into a...
Thu Nov 08, 2018 5:02 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: Induced dipoles
Replies: 2
Views: 92

### Re: Induced dipoles

If a molecule is already experiencing a dipole moment, where one area is slightly negative and another is slightly positive, then these minor charges will cause a shift in the electron cloud of nearby molecules. If a molecule (let's call it A) is near a positively charged region of another molecule ...
Thu Nov 08, 2018 4:54 pm
Forum: Trends in The Periodic Table
Topic: First, second, third, etc. Ionization energy
Replies: 4
Views: 464

### Re: First, second, third, etc. Ionization energy

Adding onto the other two comments, sometimes you will notice that at a certain point, the ionization energy from one electron to the next will make a very large jump for an atom. Take magnesium for example. Just as the others had said, the second electron requires more energy to be removed in compa...
Fri Nov 02, 2018 7:10 pm
Forum: Formal Charge and Oxidation Numbers
Topic: shortcut for FC
Replies: 6
Views: 296

### Re: shortcut for FC

The long formula for formula charge is: FC= (valence electrons) - (# lone pair electrons + (# of shared electrons / 2 ) ) The best way I can think of shortening this is by swapping (# of shared electrons / 2 ) with just the number of Lewis lines that signify bonds since each bond line represents 2 e...
Fri Nov 02, 2018 7:04 pm
Forum: Octet Exceptions
Topic: Number of Unpaired Electrons
Replies: 2
Views: 200

### Re: Number of Unpaired Electrons

The key to this is following Hund's Rule for electron configurations. We know there are 8 electrons on the 3d subshell. We also know there are 5 orbitals in the d subshell (5 possible ml values; accommodates 10 electrons). First, we can place one electron in each of the 5 orbitals. 3d: ^ ^ ^ ^ ^ Now...
Fri Nov 02, 2018 6:58 pm
Forum: Lewis Structures
Topic: Do brackets go over cations or anions or either or both?
Replies: 3
Views: 143

### Re: Do brackets go over cations or anions or either or both?

I'm not too sure about if there is a correct way of doing it, but I usually put brackets around both ions when drawing the Lewis structures.
Wed Oct 24, 2018 4:36 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Balmer, Lyman, Paschen Series
Replies: 3
Views: 229

### Re: Balmer, Lyman, Paschen Series

I haven't taken the test yet, but from my understanding, we are supposed to know the lowest energy level and the type of electromagnetic radiation each series represents.
Wed Oct 24, 2018 1:26 pm
Forum: Electron Configurations for Multi-Electron Atoms
Topic: f-orbitals
Replies: 2
Views: 155

### Re: f-orbitals

Similarly to how Professor Lavelle describes the d-orbitals as lagging by 1 period, the f-orbitals lag by 2 periods. Just as the person before me stated, the 4f orbital is placed in the same period as the 6s orbital.
Wed Oct 24, 2018 1:22 pm
Forum: Trends in The Periodic Table
Topic: Isoelectronic Clarification
Replies: 2
Views: 111

### Isoelectronic Clarification

Can somebody clarify the importance of recognizing that multiple ions can be isoelectronic? I know that isoelectronic ions don't necessarily have the same chemical properties. Do we just need to understand that they carry the same number of electrons?
Sat Oct 20, 2018 4:58 pm
Forum: Quantum Numbers and The H-Atom
Topic: ml Quantum Number and d-Orbital Orientation.
Replies: 1
Views: 195

### ml Quantum Number and d-Orbital Orientation.

Similarly to how we know that ml=-1 in the p-orbital would mean that the orbital is aligned on the x axis, would we need to know what each ml number in the d orbital corresponds to? And if so, what orientation corresponds with each ml number?
Wed Oct 17, 2018 1:04 pm
Forum: *Shrodinger Equation
Topic: Schrodinger's equation
Replies: 2
Views: 106

### Re: Schrodinger's equation

I'm pretty sure that Prof. Lavelle said that it is important to understand the concepts behind the equation, but we wouldn't be expected to use it for any calculations. Such calculations are grad level work.
Wed Oct 17, 2018 1:01 pm
Forum: Einstein Equation
Topic: Units of Energy
Replies: 5
Views: 261

### Re: Units of Energy

It is best to break down the units of a joule when you are also trying to calculate energy. Often times problems will try to trick you by giving velocity in miles/hour or they will give you mass in grams. When you approach a problem like this, it is important to know that you need values in kg and m...
Sun Oct 14, 2018 3:41 pm
Forum: Properties of Light
Topic: Units for a Joule [ENDORSED]
Replies: 3
Views: 131

### Re: Units for a Joule[ENDORSED]

I know other people already gave good explanations for the units of a joule, but I wanted to share a way to sort of remember the units. When I took AP Physics in high school, my teacher told us a little phrase to remember the units: "Newton, meter (meet her). She's a Joule (jewel)!" From p...
Wed Oct 10, 2018 1:25 pm
Forum: Bohr Frequency Condition, H-Atom , Atomic Spectroscopy
Topic: Going from Spectroscopic line to Energy levels
Replies: 1
Views: 49

### Going from Spectroscopic line to Energy levels

Hi, I am a bit confused with the idea of taking the length of the spectroscopic line and working backwards to find the beginning and ending energy levels of the electron. This confusion comes from problem 15 in chapter 1 of the 6th edition textbook. However, I want to understand this type of problem...
Tue Oct 09, 2018 5:03 pm
Forum: Photoelectric Effect
Topic: Photoelectric Experiment
Replies: 2
Views: 110

### Re: Photoelectric Experiment

After an electron is ejected from the metal, they will gravitate towards the detector because the detector has a slightly positive charge and the election has a negative charge. The detector is also connected to the metal, allowing the electron to make its way back to the metal. I assume the loss of...
Sun Oct 07, 2018 3:34 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Percision and Accuracy
Replies: 5
Views: 310

### Re: Percision and Accuracy

Another example would be a titration lab. If you were to repeat the titration lab and continued to use about the same volume of the titrant in order to activate the indicator for each trial, then your lab would have a precise set of trials. However, your lab trials would only be accurate if the stan...
Wed Oct 03, 2018 1:14 pm
Forum: Significant Figures
Topic: Sig Figs when finding Mol
Replies: 4
Views: 1538

### Re: Sig Figs when finding Mol

If the number of moles is the answer to the problem, you would want to round according to the number of sigfigs, which in this case seems to be 4 significant figures. However, if you are going to continue using the number in further calculations, you should continue using the longer version. Accordi...
Mon Oct 01, 2018 5:21 pm
Forum: Accuracy, Precision, Mole, Other Definitions
Topic: Formula Units [ENDORSED]
Replies: 3
Views: 1208

### Formula Units[ENDORSED]

While working on the textbook problems, I came across problems asking for formula units. I am still confused about what a formula unit is. Can somebody please explain it to me and how to find it?