Search found 101 matches
- Mon Mar 16, 2020 2:29 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: H2O
- Replies: 44
- Views: 2296
Re: H2O
You never include solids or liquids in the ICE table or equilibrium constants. If it's gaseous or aqueous, then it's included. In the case of H2O, the only time you would include it is if it's H2O(g).
- Mon Mar 16, 2020 2:28 pm
- Forum: Gibbs Free Energy Concepts and Calculations
- Topic: ΔGionization
- Replies: 10
- Views: 874
Re: ΔGionization
Nope! you can use any of the equations for calculating deltaG. I think it's just a way to label it relating to the reaction.
- Mon Mar 16, 2020 2:26 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: Initial vs Unique Rates
- Replies: 3
- Views: 299
Re: Initial vs Unique Rates
The initial rate is the instantaneous rate at the beginning of a reaction (this is a derivative), the unique rate uses the average rates and accounts for the stoichiometric coefficients of the reactants and products (this is not a derivative).
- Mon Mar 16, 2020 2:22 pm
- Forum: Arrhenius Equation, Activation Energies, Catalysts
- Topic: Activation Energy
- Replies: 3
- Views: 380
Re: Activation Energy
An increase in temperature doesn't affect the activation energy. In the case of an endothermic reaction, increasing the temperature causes the forward rate constant to increase because it'll be easier to overcome the energy barrier bc there will be more energy (however, the value of the barrier does...
- Mon Mar 16, 2020 2:19 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Final Grades
- Replies: 6
- Views: 645
Final Grades
Anyone have any idea when we'll get our final grades since it was all online?
- Wed Mar 11, 2020 4:34 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: residual entropy interpretation
- Replies: 2
- Views: 277
Re: residual entropy interpretation
When T = 0 K that's the absolute zero for temperature, so the molecules won't have any kinetic energy and therefore no movement, so their entropy is all based on the different positions/microstates the molecules can occupy.
- Wed Mar 11, 2020 12:39 pm
- Forum: General Rate Laws
- Topic: Instantaneous rate
- Replies: 4
- Views: 361
Re: Instantaneous rate
Yes! They're more useful than average rates since they give us the concentration at any particular point in time (this is expressed as the derivative). From the instantaneous rates, we can derive differential rate laws, integrated rate laws, etc. since they're all based on the derivatives.
- Wed Mar 11, 2020 12:31 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Review Packet
- Replies: 5
- Views: 461
Re: Review Packet
If you search up "endgame" on chemistry community there's a review packed created by one of the UAs.
- Wed Mar 11, 2020 12:28 pm
- Forum: Administrative Questions and Class Announcements
- Topic: test 2 return
- Replies: 6
- Views: 652
Re: test 2 return
Since discussions are cancelled I think our TAs will likely email them to us, but it depends on the TA i believe.
- Wed Mar 11, 2020 12:26 pm
- Forum: Balancing Redox Reactions
- Topic: Balancing basic reactions
- Replies: 8
- Views: 576
Re: Balancing basic reactions
You can also treat basic solutions like acidic ones by adding H+ and H2O as you would, and then add the same amount of OH- as the H+ (and add that amount of OH- to the other side as well). On the side where there's H+ and OH-, you can combine them to get H2O and then make sure the H2O is only on one...
- Sun Mar 08, 2020 11:24 pm
- Forum: Zero Order Reactions
- Topic: Calculus
- Replies: 10
- Views: 775
Re: Calculus
I don't think we will actually need to use calculus to solve the problems mathematically, so it's more of a conceptual thing like when it comes to understanding what the instantaneous rates mean and also how to derive the integrated rate laws from the differential rate laws. Dr. Lavelle sent an emai...
- Sun Mar 08, 2020 11:19 pm
- Forum: General Rate Laws
- Topic: General Rate Laws
- Replies: 7
- Views: 576
Re: General Rate Laws
By using the initial rates and initial concentrations of the reactants, it's easier to determine the rate law. This is because when the products start to form they can sometimes affect the rate law and change it. If we only focus on the reactants at the start of the reaction we don't have to worry a...
- Sun Mar 08, 2020 11:16 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Diagrams
- Replies: 13
- Views: 898
Re: Cell Diagrams
You add an inert metal when the species that is being reduced isn't a metal itself, or it's a nonconducting metal in which both the reactant and product are in aqueous form, instead of one in the solid phase and one in the aqueous.
- Sun Mar 08, 2020 10:04 pm
- Forum: First Order Reactions
- Topic: 7B.3
- Replies: 2
- Views: 219
7B.3
How do you find the concentration of A in part c of this question? It says: Determine the rate constant for each of the following first- order reactions, in each case expressed for the rate of loss of A: c) 2 A --> B + C [A] initial = 0.153 M and that after 115 s the concentration of B rises to 0.03...
- Sun Mar 08, 2020 7:18 pm
- Forum: Method of Initial Rates (To Determine n and k)
- Topic: How to determine the order of a reactant
- Replies: 3
- Views: 304
How to determine the order of a reactant
How do you determine the order of a species in a reaction from experimental data when there's no experiment where only the concentration of that species is changing?
- Mon Mar 02, 2020 12:54 am
- Forum: Balancing Redox Reactions
- Topic: Left and Right
- Replies: 4
- Views: 374
Re: Left and Right
By separating it into two half reactions, it's easier to balance everything and also add in species such as water or H+ if the reaction is occurring in acidic solution. Also, when you write the net ionic equation, it's easier to cancel things out in each reaction to produce the net ionic equation.
- Mon Mar 02, 2020 12:52 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: concentration related to current?
- Replies: 4
- Views: 393
Re: concentration related to current?
If you mean for a concentration cell, the solution of lower concentration will be the product because it will be increasing in concentration. The higher concentration solution will decrease in concentration, so it's the reactant. A voltage will be created as electrons flow from anode to cathode sinc...
- Mon Mar 02, 2020 12:45 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Moles in nernst
- Replies: 4
- Views: 317
Moles in nernst
For n (moles) in the nernst equation, is it the moles of electrons or the moles of the substances being oxidized/reduced?
- Sun Mar 01, 2020 9:36 pm
- Forum: Balancing Redox Reactions
- Topic: Acidic and Basic Reactions
- Replies: 9
- Views: 530
Acidic and Basic Reactions
For reactions that occur in acidic or basic solutions, why do we have to add water or H+/OH- ions, and how do we know how much to add?
- Sun Mar 01, 2020 9:29 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Salt Bridge
- Replies: 12
- Views: 720
Salt Bridge
What is the purpose of the salt bridge in a galvanic cell, and what would happen if the salt bridge wasn't a neutral salt?
- Sat Feb 22, 2020 1:22 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Clausius inequality
- Replies: 1
- Views: 267
Re: Clausius inequality
I don't think this is something we need to know for this class in particular since he never mentioned it in lecture and it doesn't appear in any homework/previous test problems.
- Sat Feb 22, 2020 1:19 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Max Potential
- Replies: 2
- Views: 216
Re: Max Potential
The max cell potential is E = -work/charge. It can also be calculated by finding the the maximum work, which is Wmax = ΔG = -nFE. They're equivalent because the max potential is related to the free energy difference between the reactants and products in a cell. This also why we can still calculate t...
- Sat Feb 22, 2020 1:13 pm
- Forum: Student Social/Study Group
- Topic: Midterm 3D
- Replies: 3
- Views: 216
Midterm 3D
Why is the net charge -1 for acetic acid? Could someone explain the reasoning behind the answer?
- Sat Feb 22, 2020 1:12 pm
- Forum: Student Social/Study Group
- Topic: Midterm 3C
- Replies: 1
- Views: 165
Midterm 3C
Could someone explain why the answer is C? I'm confused on how adding NH4Cl would lower the pH considering its ions are conjugate acids and bases.
- Sat Feb 22, 2020 1:07 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Midterm 6D
- Replies: 5
- Views: 479
Midterm 6D
I'm confused on why question 6D isn't answer choice C because going from solid to liquid would lead to an increase in entropy, and this seems to be largest relative to the other answer choices. Could someone explain this?
- Sat Feb 22, 2020 1:06 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: E cell
- Replies: 6
- Views: 499
Re: E cell
We calculate E cell using the equation Ecell = Ecathode - Eanode. Ecathode and Eanode are taken from the table of reduction potentials that will be given to us during the test.
- Sat Feb 22, 2020 12:54 pm
- Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
- Topic: Cell Diagram Example
- Replies: 3
- Views: 224
Re: Cell Diagram Example
The purpose of having the Pt is that it's an inert conductor that can transfer electrons. It's only needed when there's no conducting solids so it can do the work of moving the electrons from the anode to the cathode. Copper is a conducting solid, so the Pt isn't needed on that side. However, iron i...
- Sat Feb 22, 2020 12:46 pm
- Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
- Topic: Reversing Potentials
- Replies: 7
- Views: 452
Reversing Potentials
How do we know when we need to reverse a reduction equation (to make it oxidation) and therefore multiply the reduction potential by -1?
- Sat Feb 22, 2020 10:58 am
- Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
- Topic: Nerst Equation
- Replies: 10
- Views: 1072
Re: Nerst Equation
I don't think we ever need to know how to derive any of the equations Lavelle shows us in lecture, it's more to help us with a conceptual understanding. You just need to know the equation itself and when it's used.
- Tue Feb 11, 2020 2:45 pm
- Forum: Entropy Changes Due to Changes in Volume and Temperature
- Topic: Pizza Rolls 6
- Replies: 3
- Views: 267
Pizza Rolls 6
Can someone explain pizza rolls question 6? I'm confused on why ΔS = 0 and ΔU = 0. Also, I added up 2 calculations for the heat, but I can't seem to get the right answer. If anyone has tips on how to approach the problem please let me know!
- Sat Feb 08, 2020 4:23 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: 4C.3
- Replies: 2
- Views: 94
Re: 4C.3
My TA mentioned this in discussion and said that at constant pressure for an ideal gas, specific heat (Cp) = 5/2R. At constant volume for an ideal gas, Cv=3/2R. So for part a you would plug in 5/2R into q = nCp∆T and for part b you would plug in 3/2R into q = nCv∆T.
- Sat Feb 08, 2020 4:14 pm
- Forum: Concepts & Calculations Using Second Law of Thermodynamics
- Topic: Entropy equation
- Replies: 2
- Views: 109
Entropy equation
Can someone explain the concept behind the ∆S = q/T equation? I'm confused on what it really means and when to use it.
- Sat Feb 08, 2020 4:00 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: Error in Boltzmann Equation
- Replies: 4
- Views: 308
Error in Boltzmann Equation
I was looking at my lecture notes and in class we discussed that the Boltzmann equation has a small error for S but a large error for w. What does this mean exactly?
- Sat Feb 08, 2020 3:22 pm
- Forum: Calculating Work of Expansion
- Topic: Integral for work
- Replies: 4
- Views: 183
Integral for work
Do we actually need to calculate the integral for the work equation when the system is at equilibrium or do we just calculate using -P∆V?
- Sat Feb 08, 2020 3:20 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Calculating bond enthalpies
- Replies: 4
- Views: 145
Calculating bond enthalpies
When finding calculating bond enthalpies, do we account if there's multiple of the same bond? For example, for CH3 do we multiply the C-H bond enthalpy by 3? Also, will calculating bond enthalpies be a skill we really need to know for the test since it's the least accurate method of calculating enth...
- Fri Jan 31, 2020 4:50 pm
- Forum: Thermodynamic Systems (Open, Closed, Isolated)
- Topic: Types of Systems
- Replies: 4
- Views: 305
Re: Types of Systems
Anything that allows for energy to be exchanged with its surroundings but not matter is a closed system. One example is a pressure cooker.
- Fri Jan 31, 2020 4:42 pm
- Forum: General Science Questions
- Topic: Increasing Entropy
- Replies: 5
- Views: 396
Re: Increasing Entropy
If there's an increase an entropy due to the reaction, the universe will respond by decreasing the entropy somewhere else in order to keep entropy constant overall.
- Fri Jan 31, 2020 4:37 pm
- Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
- Topic: Textbook Question 4A.3
- Replies: 1
- Views: 73
Textbook Question 4A.3
The question says: "Air in a bicycle pump is compressed by pushing in the handle. The inner diameter of the pump is 3.0 cm and the pump is depressed 20. cm with a pressure of 2.00 atm. (a) How much work is done in the compression? (b) Is the work positive or negative with respect to the air in ...
- Fri Jan 31, 2020 11:53 am
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: 5% Rule
- Replies: 9
- Views: 378
Re: 5% Rule
If the % ionization is less than 5%, then we can use assumption and get rid of the x in the denominator since the initial and equilibrium concentrations will be very similar.
- Fri Jan 31, 2020 11:51 am
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Hess' Law
- Replies: 7
- Views: 268
Re: Hess' Law
Yes! Because enthalpy is a state property, we can add or subtract the enthalpy changes in order to get to an overall reaction since the path we take to get there doesn't matter.
- Fri Jan 24, 2020 3:13 pm
- Forum: Phase Changes & Related Calculations
- Topic: Phase Transition Temp.
- Replies: 6
- Views: 361
Re: Phase Transition Temp.
During a phase change, all the added heat energy is going towards breaking the bonds rather than increasing the temperature. Therefore, the temperature won't change.
- Fri Jan 24, 2020 3:11 pm
- Forum: Administrative Questions and Class Announcements
- Topic: homework for week 4
- Replies: 11
- Views: 447
Re: homework for week 4
Any of the problems from the Thermochemistry section of the syllabus!
- Fri Jan 24, 2020 3:07 pm
- Forum: General Science Questions
- Topic: Fall 2019 final
- Replies: 7
- Views: 250
Re: Fall 2019 final
We have to pick them up ourselves in Young Hall 3034 between 9-5pm.
- Fri Jan 24, 2020 3:04 pm
- Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
- Topic: Bond Enthalpy Accuracy
- Replies: 6
- Views: 156
Re: Bond Enthalpy Accuracy
Bond enthalpies are for breaking bonds in gases, so you need to add in the enthalpy of phases changes for reactants/products that are liquid or solid. Additionally, they're averages from many different molecules, which makes them less accurate. Using Hess's Law or the standard enthalpies would be a ...
- Fri Jan 24, 2020 12:23 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Textbook Problem 5.35
- Replies: 2
- Views: 133
Textbook Problem 5.35
5.35 says: The following plot shows how the partial pressures of reac- tant and products vary with time for the decomposition of com- pound A into compounds B and C. All three compounds are gases. Use this plot to do the following: (a) Write a balanced chemical equation for the reaction. (b) Calcula...
- Mon Jan 20, 2020 7:19 pm
- Forum: *Making Buffers & Calculating Buffer pH (Henderson-Hasselbalch Equation)
- Topic: Test 1 material
- Replies: 3
- Views: 714
Re: Test 1 material
I don't think so, considering it's not listed on Outline 2. If he doesn't mention it in class either I don't think it's something we need to know.
- Mon Jan 20, 2020 7:16 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: K
- Replies: 5
- Views: 261
Re: K
The only time K is changed is when the temperature is changed (endo/exothermic reactions). For changes in concentration or pressure, the reaction will adjust so it can eventually go back to equilibrium and therefore remain at the same K value.
- Mon Jan 20, 2020 7:12 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Coverting Kp to Kc
- Replies: 2
- Views: 109
Re: Coverting Kp to Kc
It just depends on what units the data is given in. If it's concentrations, then you would denote that with Kc, but if you're given it in pressure, then denote it with Kp. If for some reason you need to convert between concentration and pressure, you can use PV=nRT.
- Mon Jan 20, 2020 7:10 pm
- Forum: Student Social/Study Group
- Topic: Test 1
- Replies: 9
- Views: 618
Re: Test 1
There's no practice tests but if you do all the homework problems in the textbook and review your lecture notes you should be well prepared!
- Mon Jan 20, 2020 7:08 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: ICE table and X
- Replies: 6
- Views: 333
Re: ICE table and X
You can approximate when K is less than 10^-3 because the change in the initial concentration will be so small that x will be a negligible value.
- Fri Jan 10, 2020 5:28 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Change in k
- Replies: 11
- Views: 576
Re: Change in k
Because of Le Chatelier's Principle. the reaction will adjust in order to keep the ratio of products to reactants the same. For example, if there's a higher concentration of reactants, the reaction will adjust to have a higher concentration of products. The actual concentrations will change, but the...
- Fri Jan 10, 2020 5:27 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: HW 5J.5
- Replies: 8
- Views: 216
Re: HW 5J.5
The rule for changes in pressure applies to only moles of gas, so you don't consider the solid and therefore there are more moles of gas on the right, so the reaction shifts to the left and favors the reactants.
- Fri Jan 10, 2020 5:18 pm
- Forum: Non-Equilibrium Conditions & The Reaction Quotient
- Topic: Alternative Forms [ENDORSED]
- Replies: 2
- Views: 182
Re: Alternative Forms [ENDORSED]
It just depends on what unit the the products and reactants are given in. If it's in molar concentration, then the equilibrium constant is denoted as Kc. If it's given in partial pressures, then it's denoted as Kp. They both mean the same thing, but it's just to differentiate between both.
- Fri Jan 10, 2020 4:58 pm
- Forum: Applying Le Chatelier's Principle to Changes in Chemical & Physical Conditions
- Topic: Today's Lecture
- Replies: 3
- Views: 157
Re: Today's Lecture
The reasoning really comes from comparing Q (reaction quotient) to K. In the example he used, the concentration doubled due to the change in pressure, so Q < K and the reaction shifts right. There was more moles on the left, so this is consistent with the short reasoning. I wouldn't worry too much a...
- Fri Jan 10, 2020 4:51 pm
- Forum: Equilibrium Constants & Calculating Concentrations
- Topic: Pressure and Volume
- Replies: 8
- Views: 246
Re: Pressure and Volume
Changes in pressure or volume cause changes in concentration (due to PV=nRT), and changes in concentration don't affect K due to Le Chatelier's Principle, so that's why pressure and volume don't affect K, only temperature.
- Sat Dec 07, 2019 10:40 am
- Forum: Quantum Numbers and The H-Atom
- Topic: Midterm Question 6A
- Replies: 1
- Views: 120
Midterm Question 6A
For 6A on the midterm, I thought the question was asking about the quantum number l because the question mentions subshells, but what are the correct values for this question?
- Sat Dec 07, 2019 10:37 am
- Forum: Photoelectric Effect
- Topic: Midterm Question 2B
- Replies: 2
- Views: 249
Midterm Question 2B
I'm going over the midterm and I was wondering what the correct graph would look like for question 2B, and why?
- Sat Dec 07, 2019 10:32 am
- Forum: Acidity & Basicity Constants and The Conjugate Seesaw
- Topic: Ka Kb on the Final
- Replies: 2
- Views: 144
Re: Ka Kb on the Final
I don't think this is something we need to know a lot about for the final. Ka and Kb were mentioned in a review session yesterday, so I would just know the formula for calculating them and know that they relate to weak acids/bases. However, I think that most of our calculations will have to do with ...
- Sat Dec 07, 2019 10:30 am
- Forum: Lewis Acids & Bases
- Topic: About 6A.17
- Replies: 1
- Views: 97
Re: About 6A.17
Here's what my TA told me:
metals form basic oxides
nonmetals form acidic oxides
elements diagonally from Be to Po on periodic table and some d-block elements form amphoteric molecules.
so for example, SO2 would be acidic since S is a nonmetal.
metals form basic oxides
nonmetals form acidic oxides
elements diagonally from Be to Po on periodic table and some d-block elements form amphoteric molecules.
so for example, SO2 would be acidic since S is a nonmetal.
- Sat Dec 07, 2019 10:28 am
- Forum: Lewis Acids & Bases
- Topic: Acids and Bases Lists
- Replies: 1
- Views: 166
Re: Acids and Bases Lists
Yes!
Strong acids: HCl, HBr, HNO3, H2SO4, HClO4 and HI
Strong bases: oxides and hydroxides of group 1 and 2 metal cations (e.g. NaOH, CaO)
Strong acids: HCl, HBr, HNO3, H2SO4, HClO4 and HI
Strong bases: oxides and hydroxides of group 1 and 2 metal cations (e.g. NaOH, CaO)
- Sat Dec 07, 2019 10:25 am
- Forum: Lewis Acids & Bases
- Topic: formic acid
- Replies: 1
- Views: 214
Re: formic acid
The methyl group on acetic acid is electron donating and stabilizes the structure of the compound more, and this also destabilizes the negative charge on the conjugate base. If the conjugate base is less stable, then the corresponding acid is less acidic. Formic acid has a hydrogen attached rather t...
- Sat Dec 07, 2019 10:10 am
- Forum: Identifying Acidic & Basic Salts
- Topic: Identifying Acidic and Basic Salts
- Replies: 3
- Views: 309
Re: Identifying Acidic and Basic Salts
You can also look at the ions and see if they're conjugate acids/bases of strong or weak acids/bases. For example, if the ions are the conjugate acid and base of a strong acid and a strong base, then you will know the salt is neutral.
- Sat Dec 07, 2019 10:05 am
- Forum: Lewis Acids & Bases
- Topic: 6A.17
- Replies: 1
- Views: 114
Re: 6A.17
My TA told me these rules:
metals form basic oxides
nonmetals form acidic oxides
elements diagonally from Be to Po and some d-block elements form amphoteric molecules
so for example, SO2 is acidic because S is a nonmetal.
metals form basic oxides
nonmetals form acidic oxides
elements diagonally from Be to Po and some d-block elements form amphoteric molecules
so for example, SO2 is acidic because S is a nonmetal.
- Sat Dec 07, 2019 10:03 am
- Forum: Conjugate Acids & Bases
- Topic: studying
- Replies: 7
- Views: 661
Re: studying
My TA told me our main focus should be strong acids and bases, but doing the homework problems and reading the textbook sections is what I'm doing to study.
- Sat Dec 07, 2019 9:59 am
- Forum: Calculating pH or pOH for Strong & Weak Acids & Bases
- Topic: 2oh- and oh-
- Replies: 1
- Views: 115
Re: 2oh- and oh-
Yeah it depends on the compound you're working with, so you have to think about how lone pairs or protons are being donated. For an oxide like CaO, you end up with 2 OH- because the oxygen takes a hydrogen from water so you form 2 OH-.
- Sat Nov 16, 2019 1:53 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: All VSEPR structures or just ones from class?
- Replies: 11
- Views: 699
Re: All VSEPR structures or just ones from class?
I would remember all of them just to be safe. My TA sent a chart he made with the shapes and there's more variations on there then we went over in class.
- Sat Nov 16, 2019 1:49 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: Dipole Moments
- Replies: 1
- Views: 112
Re: Dipole Moments
You need to draw the arrow with the plus on one end, which the arrow pointing towards the more electronegative atom and the plus side towards the less electronegative atom. You can also draw the partial negatives and positives using a lowercase sigma. Do this for every bond on your structure and the...
- Sat Nov 16, 2019 1:46 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Acids and Bases
- Replies: 4
- Views: 228
Re: Acids and Bases
I don't think this is something we need to know for Test 2, it's just going to cover anything after the midterm which includes Topic 3F (intermolecular forces) and VSEPR.
- Sat Nov 16, 2019 1:45 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 9
- Views: 571
Re: Bond Angles
Maya Pakulski 3D wrote:So we basically just have to memorize which bond angles go with which shapes?
Yes that's honestly the easiest way, but conceptually you should know that the reason the bond angles occur is due to repulsion between lone pairs and bonding pairs.
- Sat Nov 16, 2019 1:43 pm
- Forum: Determining Molecular Shape (VSEPR)
- Topic: Bond Angles
- Replies: 3
- Views: 244
Re: Bond Angles
You should know where the bond angles are in the structures if there's multiple. For example, in trigonal bipyramidal, you should know the 120 bond angles are between the 3 atoms in the same plane, the 90 degree angles are between the trigonal plane and the atoms above and below, and there's a 180 a...
- Fri Nov 08, 2019 3:36 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: Dispersion forces
- Replies: 6
- Views: 259
Re: Dispersion forces
The dispersion depends on the polarizability because the the more polarizable an atom is, the more it'll affect the electron density and the more the electrons will be attracted to each other. Therefore, there will be a larger fluctuation in the dipoles and the potential energy of the interaction wi...
- Fri Nov 08, 2019 3:07 pm
- Forum: Resonance Structures
- Topic: Formal Charge Question
- Replies: 16
- Views: 952
Re: Formal Charge Question
They should just sum up to the overall charge! For example if your structure is an ion that has a charge of -2, the formal charges should add up to that. But the formal charges on the atom for each resonance structure will vary because the bonds vary.
- Fri Nov 08, 2019 3:02 pm
- Forum: Lewis Structures
- Topic: Midterm grades
- Replies: 26
- Views: 1531
Re: Midterm grades
Lavelle said in lecture today that they'll be given back next Wednesday during lecture!
- Fri Nov 08, 2019 3:00 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: Iterionic and Intermolecular force difference
- Replies: 1
- Views: 103
Re: Iterionic and Intermolecular force difference
Interionic forces are between ions, which are charged molecules, and intermolecular forces are between molecules, which are covalently bonded. The interionic forces are ion-ion and ion-dipole, and the IMFs are van der waals forces and hydrogen bonding.
- Mon Nov 04, 2019 9:09 pm
- Forum: Resonance Structures
- Topic: 2B.15
- Replies: 1
- Views: 208
2B.15
The question is: Draw the Lewis structures that contribute to the resonance hybrid of nitryl chloride, ClNO2 (N is the central atom). I'm confused as to why there even needs to be resonance structures if both oxygens can have double bonds since nitrogen has enough electrons for it... is there a reas...
- Thu Oct 31, 2019 7:20 pm
- Forum: Student Social/Study Group
- Topic: Midterm
- Replies: 7
- Views: 532
Re: Midterm
There's going to be 8 questions (with parts i'm assuming) and it covers up to Outline 3 topic 2D. I think the best way to get an idea of knowing what the questions will be like is looking at your discussion section questions and also going to Lavelle's review session of past exam questions.
- Thu Oct 31, 2019 7:14 pm
- Forum: Lewis Structures
- Topic: Sulfur Dioxide
- Replies: 2
- Views: 154
Re: Sulfur Dioxide
I would always choose the structure that has the lowest formal charge, since that's what we were taught in lecture/discussion. Also, we wouldn't know what the experimental evidence is for a structure on the test so just go by the FC!
- Thu Oct 31, 2019 7:10 pm
- Forum: DeBroglie Equation
- Topic: Question about Converting Units
- Replies: 3
- Views: 146
Re: Question about Converting Units
1 eV = 1.60e-19 J, so convert from keV to eV to joules (dimensional analysis is easiest).
- Thu Oct 31, 2019 7:09 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm
- Replies: 16
- Views: 786
Re: Midterm
I'm planning on doing all the textbook questions in the syllabus for the review, quantum, and chemical bonds. This should cover everything!
- Thu Oct 31, 2019 7:08 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm
- Replies: 16
- Views: 786
Re: Midterm
I'm planning on doing all the textbook questions in the syllabus for the review, quantum, and chemical bonds. This should cover everything!
- Thu Oct 31, 2019 1:20 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Help with Textbook problem G.7
- Replies: 1
- Views: 257
Help with Textbook problem G.7
Not sure why I'm having trouble with this but I need some help on 7 from the textbook:
You need to prepare 510. g of an aqueous solution containing 5.45% KNO3 by mass. Describe how you would prepare the solution and what mass of each component you would use.
You need to prepare 510. g of an aqueous solution containing 5.45% KNO3 by mass. Describe how you would prepare the solution and what mass of each component you would use.
- Fri Oct 25, 2019 9:49 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: second quantum number
- Replies: 2
- Views: 116
Re: second quantum number
Yes the number matters here! The l = 0 always refers to the s-orbital, no matter what shell it's in. So l is always the same for each type of orbital.
- Fri Oct 25, 2019 9:47 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: 1D 15
- Replies: 2
- Views: 93
Re: 1D 15
The principal quantum number refers to the shell and the orbital angular momentum number refers to which orbital the electron is in.
So for this problem it would be:
a) 6p - n = 6, l = 1
b) 3d - n = 3, l = 2
c) 2p - n = 2, l = 1
d) 5f - n = 5, l = 3
So for this problem it would be:
a) 6p - n = 6, l = 1
b) 3d - n = 3, l = 2
c) 2p - n = 2, l = 1
d) 5f - n = 5, l = 3
- Fri Oct 25, 2019 9:44 pm
- Forum: Formal Charge and Oxidation Numbers
- Topic: Expanded Valence Shells
- Replies: 5
- Views: 250
Re: Expanded Valence Shells
They normally don't have electrons in the d-orbital, but because they have a n=3, the d-orbital exists and is available to them to fill up with more than 8 electrons, which allows them to have an expanded octet.
- Fri Oct 25, 2019 9:42 pm
- Forum: Ionic & Covalent Bonds
- Topic: Meaning of Brackets
- Replies: 7
- Views: 389
Re: Meaning of Brackets
Instead of writing out the entire electron configuration starting at 1s for an element, using the brackets of the closest previous noble gas is a shortcut and the configuration for an element will continue from there.
- Fri Oct 25, 2019 9:40 pm
- Forum: Administrative Questions and Class Announcements
- Topic: Midterm Topics
- Replies: 5
- Views: 249
Midterm Topics
Does anyone know what topics the midterm will cover? Will the high school review content from test 1 be on it too?
- Sat Oct 19, 2019 9:23 pm
- Forum: Properties of Light
- Topic: 1A. 15
- Replies: 3
- Views: 197
Re: 1A. 15
I started off by finding the frequency using the wavelength and then I used the equation: frequency = -R[1/(n1)^2- 1/(n2)^2] and solved for n1, which should get you a number close to 3. I figured out n2 because the question mentioned UV radiation, which equates to the Lyman series and n2 is always 1...
- Sat Oct 19, 2019 9:17 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Magnetic Spin
- Replies: 4
- Views: 194
Re: Magnetic Spin
I don't think it's something we really have to know for the test, since each electron has one of those spin numbers. Not totally sure on why it's +/- 1/2, but I think it's because of a theorem, which we definitely don't need to know. I would just remember that it exists and is a way of specifying a ...
- Sat Oct 19, 2019 9:15 pm
- Forum: Quantum Numbers and The H-Atom
- Topic: Values of l
- Replies: 2
- Views: 156
Re: Values of l
It's not that l has multiple possible values, but ml does. l represents the different subshells in an energy level (e.g. l = 2 represents the d subshell). This mean the values of ml for the d subshell can be -2, -1, 0, 1, 2. These values represent the 5 different orbitals of the d subshell.
- Sat Oct 19, 2019 9:12 pm
- Forum: Electron Configurations for Multi-Electron Atoms
- Topic: Homework 1E.7
- Replies: 3
- Views: 140
Re: Homework 1E.7
Yes! This matters because it violates Hund's rule, which states not only that each orbital is occupied by a single electron first, but also that all the unpaired electrons need to have parallel spins (the same spin direction).
- Sat Oct 19, 2019 9:09 pm
- Forum: Wave Functions and s-, p-, d-, f- Orbitals
- Topic: Shell, Subshell, Orbital Terminology
- Replies: 8
- Views: 578
Re: Shell, Subshell, Orbital Terminology
I was super confused about this in class at first too but this is really helpful! Thanks so much for the tip!
- Fri Oct 11, 2019 10:40 pm
- Forum: Einstein Equation
- Topic: Variables in equations
- Replies: 4
- Views: 214
Re: Variables in equations
The "v" for frequency isn't really a v but a greek letter, so I think of it more like a 'wavy' v and try to make it clear in my work. It's also helpful to know which equations use frequency and which use velocity off the top of your head.
- Fri Oct 11, 2019 10:36 pm
- Forum: Properties of Electrons
- Topic: Clarification on particle vs wave properties
- Replies: 3
- Views: 269
Clarification on particle vs wave properties
Can someone clarify or give examples of what the particle properties of an electron are and what its wavelike properties are? I feel like there are certain experiments that show each but I'm confused on what these properties are.
- Fri Oct 11, 2019 10:33 pm
- Forum: Properties of Electrons
- Topic: Wave Properties of Electrons
- Replies: 4
- Views: 299
Re: Wave Properties of Electrons
Destructive interference refers to when two waves collide "out-of-phase" in that the peak of one wave interacts with the trough of another, resulting in a smaller, weaker wave. Basically you can think of two waves that don't line up.
- Fri Oct 11, 2019 10:30 pm
- Forum: Properties of Electrons
- Topic: Energy levels
- Replies: 3
- Views: 233
Re: Energy levels
I find that it's not really necessary since the question usually just involves the numbers. Just make sure to keep track of which energy level is the final one and which one is the initial, so a diagram might help you in that aspect.
- Tue Oct 08, 2019 3:38 pm
- Forum: Molarity, Solutions, Dilutions
- Topic: Help with Textbook problem G.21
- Replies: 2
- Views: 212
Help with Textbook problem G.21
The question is: "A solution is prepared by dissolving 0.500 g of KCl, 0.500 g of K2S, and 0.500 g of K3PO4 in 500. mL of water. What is the concentration in the final solution of (a) potassium ions; (b) sulfide ions?" I calculated the molarity of the solution, but how do I find the concen...
- Wed Oct 02, 2019 11:19 am
- Forum: SI Units, Unit Conversions
- Topic: Question about Showing Work
- Replies: 22
- Views: 1121
Re: Question about Showing Work
I asked my TA specifically about balancing equations and he said you don't have to show it step by step if you just can see it and know how to balance it. Some questions have parts that make you go step by step, but I think you should just show as much work as you personally need. He did emphasize t...
- Wed Oct 02, 2019 11:17 am
- Forum: Administrative Questions and Class Announcements
- Topic: First Test in Discussion
- Replies: 13
- Views: 821
Re: First Test in Discussion
The first test has to do with the modules that review high school chem.
So the topics are:
Empirical and Molecular Formulas
Balancing Chemical Equations
Limiting Reactant Calculations
Molarity and Dilution of a Solution
So the topics are:
Empirical and Molecular Formulas
Balancing Chemical Equations
Limiting Reactant Calculations
Molarity and Dilution of a Solution
- Wed Oct 02, 2019 11:15 am
- Forum: Empirical & Molecular Formulas
- Topic: Homework problem E1
- Replies: 9
- Views: 401
Re: Homework problem E1
Basically it's asking the for the length of a chain of 1 mol of atoms strung together. Since there's 6.02 x 10^23 atoms in a mol (avogadro's number), you would multiply the radius of one Ag atom by the number of atoms in 1 mol, which gives you the total length.
- Wed Oct 02, 2019 11:12 am
- Forum: Administrative Questions and Class Announcements
- Topic: Tips for Tests [ENDORSED]
- Replies: 4
- Views: 326
Tips for Tests [ENDORSED]
Hi, just wondering if anyone has tips for studying for Lavelle's tests? I know there are plenty of practice problems in the textbook, but is there anything else/other resources people recommend doing? Thanks!