## Search found 38 matches

Fri Mar 16, 2018 8:59 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: electrode surface area and voltage
Replies: 1
Views: 413

### electrode surface area and voltage

Does increasing the service area of an electrode decrease the cell potential? Or does this not affect the cell potential
Thu Mar 15, 2018 12:48 pm
Forum: Interesting Applications: Rechargeable Batteries (Cell Phones, Notebooks, Cars), Fuel Cells (Space Shuttle), Photovoltaic Cells (Solar Panels), Electrolysis, Rust
Topic: 14.101
Replies: 4
Views: 637

### Re: 14.101

0.0257 is when you are using ln, 0.05916 is when you are using log.
Thu Mar 15, 2018 12:47 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Cell Diagram Question from Wednesday's (03/15/18) Lecture
Replies: 2
Views: 199

### Re: Cell Diagram Question from Wednesday's (03/15/18) Lecture

I think that for the purposes of this class, if two things are in the same state, we should separate them with a comma. So in this situation Ag(s) and AgBr(s) should be separated by a comma.
Wed Mar 14, 2018 4:31 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 15.65, part c
Replies: 3
Views: 295

### 15.65, part c

15.65 For the reversible, one-step reaction 2 A ---> B + C, the forward rate constant for the formation of B is 265 L/(mol*min) and the rate constant for the reverse reaction is 392 L/(mol*min). The activation energy for the forward reaction is 39.7 kJ mol 1 and that of the reverse reaction is 25.4 ...
Sat Mar 10, 2018 5:23 pm
Forum: Thermodynamic Systems (Open, Closed, Isolated)
Topic: The universe as a thermodynamic system [ENDORSED]
Replies: 3
Views: 343

### Re: The universe as a thermodynamic system[ENDORSED]

The universe is actually considered an isolated system. Since we know that energy can neither be created nor destroyed, only transformed, the universe must be an isolated system.
Sat Mar 10, 2018 5:21 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Slow Reaction
Replies: 3
Views: 186

### Re: Slow Reaction

To add to what the person above said, it also usually is the step with that has a buildup quantity of its starting reactant. The reactant is present in large amounts, so we know that the rate of the slow reaction is dependent on the reaction itself, not due to a lack of reactants.
Sat Mar 10, 2018 5:17 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Pseudo Rate Law [ENDORSED]
Replies: 3
Views: 308

### Re: Pseudo Rate Law[ENDORSED]

Problem 15.30 is a pseudo-rate law problem. I think we mostly just need to understand this topic conceptually though.
Tue Mar 06, 2018 6:48 pm
Forum: First Order Reactions
Topic: 15.99, linear plots
Replies: 1
Views: 153

### 15.99, linear plots

question 15.99 has multiple parts, one of which asks if the plot with the following description is linear: initial rate against [A] for a reaction that is first order in A

Why would this plot be linear? Thanks
Tue Mar 06, 2018 4:20 pm
Forum: General Rate Laws
Topic: 15.3
Replies: 4
Views: 310

### 15.3

15.3 In 20. s, the concentration of nitrogen dioxide, NO2, decreases from 450 mmol L 1 to 320 mmol L 1 in the reaction 2 NO2(g)--> 2 NO(g) + O2(g). (a) Determine the rate of reaction of NO2. Why is the correct answer a positive value, and not negative? shouldn't it be a negative value since the reac...
Mon Mar 05, 2018 5:21 pm
Forum: General Rate Laws
Topic: Test 3 material
Replies: 6
Views: 395

### Test 3 material

What is the last day of lecture that was for test 3? Will Friday's lecture (on pseudo rate laws and rxn mechanisms) be on the test?
Sat Mar 03, 2018 3:38 pm
Forum: Method of Initial Rates (To Determine n and k)
Topic: Importance of n and k
Replies: 2
Views: 225

### Re: Importance of n and k

The order of the reaction, n, can tell us a lot about the type of reaction we are dealing with. For example, if n=0, a zeroth order reaction, we know that the reaction proceed at a constant rate regardless of the time that has passed--this is often the case when an enzyme is fully saturated. But, if...
Sat Mar 03, 2018 3:33 pm
Forum: General Rate Laws
Topic: rate law
Replies: 3
Views: 220

### Re: rate law

Yes, to add to what the person before me said, your equation for the rate law should look something like this: Rate=k[A]^n [B]^m
Sat Mar 03, 2018 3:30 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Learning Models [ENDORSED]
Replies: 1
Views: 154

### Re: Learning Models[ENDORSED]

I found these explanations online which helped me understand this better: According to the collision model, a chemical reaction can occur only when the reactant molecules, atoms, or ions collide with more than a certain amount of kinetic energy (i.e. temperature) and in the proper orientation. The c...
Sat Feb 24, 2018 3:56 pm
Forum: Kinetics vs. Thermodynamics Controlling a Reaction
Topic: Gas in Products [ENDORSED]
Replies: 2
Views: 216

### Re: Gas in Products[ENDORSED]

Yes, I believe so. I don't think that a gas on the products side necessarily means ALL of it will leave the system, but generally speaking gas will not stay in liquid. So yes, the reverse reaction will be a lot less likely when there is a gas in the products.
Tue Feb 20, 2018 2:33 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.97-cathode vs anode
Replies: 2
Views: 122

### 14.97-cathode vs anode

14.97 Use the data in Appendix 2B and the fact that, for the half- reaction F2(g) + 2 H+ (aq) + 2e- ---> 2 HF(aq), E =3.03 V, to calculate the value of Ka for HF. Can someone please explain how I can determine if the given half reaction is for the cathode or the anode? I am confused on how to determ...
Mon Feb 19, 2018 6:00 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.31c
Replies: 1
Views: 151

### 14.31c

14.31 Identify the reactions with K>1 in the following list and, for each such reaction, identify the oxidizing agent and calculate the standard cell potential. (c) 2 Pb^2(aq)--->Pb(s)+ Pb^4+(aq) Can someone please explain how to determine which of the two half reactions is for the anode and which i...
Mon Feb 19, 2018 4:08 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: 14.23a, cell diagram
Replies: 1
Views: 158

### 14.23a, cell diagram

For part a, there is Pt(s) on the right side of the diagram, but not the left. Why is this?

Also, how do you generally know when to put Pt on one side of the diagram, both, or neither? thanks
Sun Feb 18, 2018 10:57 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Electrochemical Series Definition
Replies: 4
Views: 290

### Re: Electrochemical Series Definition

The Electrochemical Series is a table of various metals in the order of their electrochemical activities (based on their standard oxidation-reduction potentials). The most negative E° values are placed at the top of the list, and the most positive at the bottom.
Sun Feb 18, 2018 10:55 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: The Daniell Cell
Replies: 4
Views: 238

### Re: The Daniell Cell

I think the Daniell Cell is just one specific type of electrochemical cell that we can use as a basis for doing different problems that involve electrochemical cells/redox reactions. As long as you understand why/how the Daniell Cell works, you can apply these ideas to any similar electrochemical ce...
Sun Feb 18, 2018 10:50 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: galvanic vs electrolytic
Replies: 4
Views: 188

### Re: galvanic vs electrolytic

A galvanic cell converts chemical energy into electrical energy; an electrolytic cell drives a non-spontaneous redox reaction through the application of electrical energy.
Sun Feb 11, 2018 8:15 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Test #7
Replies: 7
Views: 434

### Re: Test #7

Does anyone have the correct final answer to this problem? I did the problem correctly but got the wrong final number
Thu Feb 08, 2018 9:32 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: conceptual entropy questions
Replies: 5
Views: 353

### conceptual entropy questions

The solutions manual for problem 9.27 says that HBr has a higher molar entropy than HF. Can someone please explain why this is true? Also, it states for problem 9.31 that Iodine gas has a higher molar entropy than Bromine gas, because it has a larger mass. Wouldn't smaller atoms have a higher entrop...
Thu Feb 08, 2018 8:58 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: textbook problem 9.25
Replies: 1
Views: 191

### textbook problem 9.25

9.25 If SO2F2 adopts a positionally disordered arrangement in its crystal form, what might its residual molar entropy be? I am not sure how to approach this problem. Can someone please explain to me the difference between "positionally disordered arrangement" and "residual entropy&quo...
Thu Feb 08, 2018 8:29 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Circumstances of delta G
Replies: 3
Views: 223

### Re: Circumstances of delta G

When deltaG=0, K is equal to one. This means that the reaction is at equilibrium, and the products/reactants are equally favored.

When deltaS=0, we would be talking about a perfect crystal, where there is only one possible state that each particle can be in.
Thu Feb 08, 2018 8:25 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 11.83
Replies: 2
Views: 171

### Re: 11.83

The ΔGf° of a substance has to do with the reaction where the substance is formed from the elements that exist in their most stable forms at a pressure of 1 atm and, most of the time, 298K. Once we have a different temperature than the "standard" one for the specific element, we can no lon...
Thu Feb 08, 2018 8:22 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: 9.65
Replies: 3
Views: 183

### Re: 9.65

I think its because the question is asking specifically about a temperature change with only has to do with the TdeltaS term, not the deltaH term. It's asking with respect to only temperature, not the entire Gibbs free energy equation.
Mon Jan 29, 2018 6:13 pm
Forum: Administrative Questions and Class Announcements
Replies: 3
Views: 316

Is there any rough guideline as to what textbook reading/homework problems we should do each week to be keeping up with class lectures? Also, can homework 4 (due this week) include problems from ch 8 that have to do with calculating work/internal energy, or should the problems only be from chapter 9...
Mon Jan 29, 2018 6:04 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: estimating an entropy change
Replies: 2
Views: 163

### estimating an entropy change

Self-Test 9.13B: "Without doing any calculations, estimate the sign of the entropy change of the system for the reaction CaCO3(s) --> CaO(s) + CO2(g) and explain your answer" Can someone please guide me through this question? Can I just assume that delta S is positive, since there is a gas...
Mon Jan 29, 2018 5:59 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: entropy of heavy vs. light molecules
Replies: 2
Views: 228

### entropy of heavy vs. light molecules

In figure 9.13 in the textbook, the caption states the following: "The energy levels of a particle in a box are more widely spaced for (a) light molecules than for (b) heavy molecules. As a result, the number of thermally accessible levels, as shown by the tinted band, is greater for heavy mole...
Thu Jan 25, 2018 5:05 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: 8.41
Replies: 2
Views: 231

### Re: 8.41

If you remember Dr. Lavelle's lecture slide from class, is said that "qsys=-qsurroundings." In this case, you can kind of think of the ice as the "system" and the water is the "surroundings." So, you would set the heat needed to melt the ice+the heat needed to raise the...
Thu Jan 25, 2018 4:59 pm
Forum: Phase Changes & Related Calculations
Topic: Change in internal energy as a state function
Replies: 2
Views: 905

### Re: Change in internal energy as a state function

So depending on the process by which a system gets from its initial to its final state, the amount of energy transferred by heat/work methods can vary. The distribution of energy transfer between heat and work depends on the process. This is why we say heat and work are "path-dependent." O...
Thu Jan 25, 2018 4:53 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: The sign of q
Replies: 5
Views: 403

### Re: The sign of q

Yes, you are correct that this is an exothermic reaction and the system is releasing energy. The statement "qsys=-qsurroundings" is just to help us solve for the missing variable. This statement though is the equivalent of saying that "-qsys=qsurroundings." What one gains is what...
Mon Jan 15, 2018 10:03 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Homework 8.29
Replies: 5
Views: 287

### Re: Homework 8.29

In addition to what has already been said, you can think about the fact that NO2 has more bonds than NO. This means that for a given amount of energy that is applied toward breaking the bonds, the energy is absorbed by 4 bonds (in NO2) as opposed to just 2 bonds (in NO). So, it will take more energy...
Mon Jan 15, 2018 9:59 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: rxn enthalpy vs. rxn internal energy
Replies: 1
Views: 114

### rxn enthalpy vs. rxn internal energy

Why is the reaction enthalpy less negative (more positive) than the reaction internal energy for reactions that generate gases? I am having trouble understanding this idea. Thanks.
Mon Jan 15, 2018 12:04 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Heat capacity at constant pressure vs. constant volume [ENDORSED]
Replies: 1
Views: 181

### Heat capacity at constant pressure vs. constant volume[ENDORSED]

Can someone please explain to me why the molar heat capacity of an ideal gas at constant pressure is greater than that at constant volume? Thank you.
Fri Jan 12, 2018 4:37 pm
Forum: Phase Changes & Related Calculations
Topic: Why can state properties be added?
Replies: 11
Views: 714

### Re: Why can state properties be added?

When it comes to state properties, the path taken to get from point A to point B does not matter. The link: https://chem.libretexts.org/Core/Physical_and_Theoretical_Chemistry/Thermodynamics/State_Functions gave an example that really helped me understand this concept better. Here is one of the part...
Fri Jan 12, 2018 4:25 pm
Forum: Phase Changes & Related Calculations
Topic: Clarification
Replies: 3
Views: 234

### Re: Clarification

While enthalpy is a state function, heat is not. So, you can calculate enthalpy by simply doing (final-initial). On the other hand, heat is not a state function. Heat is defined by the path it takes to get from point 1 to point 2, which is why we can't treat it like a state function.
Fri Jan 12, 2018 4:18 pm
Forum: Phase Changes & Related Calculations
Topic: Isothermal Expansion
Replies: 2
Views: 228

### Isothermal Expansion

I understand that isothermal expansion implies constant temperature while volume is increasing and pressure is decreasing. Can someone please explain the role of the work function in this concept?