## Search found 31 matches

Tue Mar 13, 2018 1:53 pm
Forum: Reaction Mechanisms, Reaction Profiles
Topic: HW 15.85
Replies: 2
Views: 128

### Re: HW 15.85

I believe the dots are essentially representing the bonds that are broken, although I am not completely sure. I think you could also put a line to represent the bonds breaking or forming in the activated complex.
Mon Mar 12, 2018 9:37 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Chapter 14 #117
Replies: 1
Views: 94

### Chapter 14 #117

This problem asks us to find the current, given delta G and the reduction half reaction. In the solutions manual, it says It=nF=delta G/-E. How do we know that current x time is equal to delta G/-E? Are we supposed to find this through units or another way (or would we be given the equation)?
Mon Mar 12, 2018 8:45 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Chapter 9 #69
Replies: 1
Views: 131

### Chapter 9 #69

This problem asks us what amount of moles of ATP could be formed if the Gibbs free energy released in the oxidation of 3 moles NADH were used to generate ATP? Given the three reactions in the problem, I understand why we must multiply the Gibbs free energy of reaction 2 by 3 moles, but we do we also...
Thu Mar 08, 2018 2:32 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Chapter 15 #85
Replies: 2
Views: 129

### Chapter 15 #85

This problem asks for us to draw a proposed structure for the activated complex. What are the steps to do this? I'm not quite sure I understand the solutions in the solutions manual and the method to get them.
Tue Mar 06, 2018 6:57 pm
Forum: General Rate Laws
Topic: 15.3
Replies: 3
Views: 148

### Re: 15.3

The concentrations you are given are in terms of NO2 so there is no need to convert them as we are finding the rate of reaction in terms of NO2. You can see that in part b, you must use the coefficients to find the rate of formation of O2.
Tue Mar 06, 2018 5:57 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: 9.61
Replies: 2
Views: 113

### Re: 9.61

The solutions manual changed the format of how they were calculating the value that describes the change in temperature. For me, it just made it more confusing so I did it as (1/T1 - 1/T2) and still got the same answer, so I would just suggest doing the method that is the easiest for you! Either way...
Mon Mar 05, 2018 7:41 pm
Forum: Arrhenius Equation, Activation Energies, Catalysts
Topic: Chapter 15 #79
Replies: 1
Views: 102

### Chapter 15 #79

This question describes how two or more different products can be formed by different pathways, and whether kinetic control or thermodynamic control predominates. Is it just based on temperature and the activation energy barrier or how do we know which dominates? I'm not quite clear on this concept.
Thu Mar 01, 2018 6:18 pm
Forum: General Rate Laws
Topic: nth order reactions [ENDORSED]
Replies: 2
Views: 109

### nth order reactions[ENDORSED]

I know we generally won't be dealing with reactions other than zeroth order, first order, and second order, but how would the graphs look for reactions to higher orders or to an order such as 1.5? What would the significance of this be chemically?
Thu Mar 01, 2018 6:13 pm
Forum: Zero Order Reactions
Topic: Zero Order Reactions and Catalysts
Replies: 2
Views: 125

### Zero Order Reactions and Catalysts

For zero order reactions, the rate of the reaction is independent on the concentration of the reactants. In lecture, I believe Dr. Lavelle mentioned something about how zero order reactions often occur when a catalyst or enzyme is required. I'm not quite sure why zero order reactions are especially ...
Thu Mar 01, 2018 6:08 pm
Forum: First Order Reactions
Topic: 15.27
Replies: 6
Views: 311

### Re: 15.27

For parts a) and b), you can also multiply the half-life by 3 for a) and 2 for b) since when 1/8 is remaining is the time elapsed for 3 half-lives ( (1/2)^3) and since 1/4 remaining is the time elapsed for 2 half-lives ( (1/2)^2). However, for parts c) and d), you must solve using the equations.
Tue Feb 20, 2018 8:10 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Chapter 14 #33
Replies: 1
Views: 112

### Chapter 14 #33

This question asks whether Tl+ will disproportionate in aqueous solution. I am not really clear on how to determine whether something will disproportionate or not, is there any easier way to understand this than what's in the solutions manual?
Tue Feb 20, 2018 2:07 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.35
Replies: 2
Views: 114

### Re: 14.35

It should be 1, there is an error in the solution manual. Check the link called "Errors in Solution Manual" on Dr. Lavelle's website to see the correct solution.
Tue Feb 20, 2018 12:46 pm
Forum: Galvanic/Voltaic Cells, Calculating Standard Cell Potentials, Cell Diagrams
Topic: Chapter 14 #25
Replies: 1
Views: 68

### Chapter 14 #25

For this problem, we are asked to arrange the metals in order of increasing strength as reducing agents. From what I understand, the stronger reducing agents have more negative standard reduction potentials. Why is Cr said to be stronger than Zn then?
Tue Feb 13, 2018 5:18 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: What does n represent?
Replies: 2
Views: 148

### Re: What does n represent?

The value of n represents the number of moles of the substance in the problem. Usually in these types of problems, the moles will not change as it's only the temperature, pressure, or volume that is changing.
Tue Feb 13, 2018 5:15 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Practice Midterm #6b
Replies: 2
Views: 107

### Practice Midterm #6b

This problem says that it is false that we would expect an endothermic reaction to be favorable at a high temperature. When I tried to reason this, I said that delta H is positive (enthalpy increases) and delta S is positive (entropy increases), so at a high temperature, delta G would be negative an...
Tue Feb 13, 2018 1:24 pm
Forum: Phase Changes & Related Calculations
Topic: Exothermic Reaction
Replies: 3
Views: 155

### Exothermic Reaction

When a reaction is exothermic, you are removing heat from the system. Why doesn't the temperature of the system always decrease if you are removing heat?
Tue Feb 06, 2018 8:15 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.33
Replies: 1
Views: 91

### Re: 9.33

If the moles of gas decreases from reactants to products, then the entropy decreases, which is why we can say entropy decreases for this reaction. However, I'm not sure that if the moles overall decreases that we can assume the entropy decreases.
Tue Feb 06, 2018 8:10 pm
Forum: Balancing Redox Reactions
Topic: Transition Metals
Replies: 4
Views: 136

### Re: Transition Metals

Often times you can tell their oxidation states based off what other elements are in the compound. For example, in the example in the lecture, we see that permanganate is MnO4-. Since we know that oxygen is -2, we can tell that Mn is +7 by looking at the overall charge and number of oxygen elements.
Mon Feb 05, 2018 6:24 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Chapter 11 #17
Replies: 2
Views: 96

### Chapter 11 #17

For some reason, I am getting -2.7 kJ/mol for the answer to the problem, but the solutions manual says -27 kJ/mol. My calculations seem to be the same as in the solutions manual, so I was wondering if there's any conversions or anything I'm missing here?
Sat Feb 03, 2018 9:18 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Gibb's Free Energy
Replies: 2
Views: 89

### Gibb's Free Energy

What is the main difference between Gibbs free energy of reaction and the standard Gibbs free energy of reaction? I get that the second is in terms of standard molar Gibbs energies, but in lecture, we said that when Gibbs free energy of reaction = 0 the reaction is at equilibrium, but when the stand...
Sat Feb 03, 2018 8:27 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: When to use Q versus K [ENDORSED]
Replies: 6
Views: 471

### Re: When to use Q versus K[ENDORSED]

K is the ratio of concentration of products to concentration of reactants when the reaction is at equilibrium. Q is the ratio when the reaction is not at equilibrium. Therefore, you would use K when at equilibrium, and Q when not at equilibrium.
Thu Feb 01, 2018 5:17 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Change of Entropy for V and T
Replies: 2
Views: 103

### Re: Change of Entropy for V and T

If you consider the equation PV=nRT, you can see that pressure (P) and volume (V) are inversely proportional. Because they are inversely proportional, when you substitute P for V, the ratio is switched.
Tue Jan 23, 2018 1:25 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimeters
Replies: 1
Views: 83

### Re: Calorimeters

A calorimeter is a device used to measure heat of reaction, whether the heat is given off or absorbed by the reaction. It functions by putting the reactants in a thermally insulated container and then measuring the rise in temperature due to the amount of heat produced. Specific heat capacity can th...
Tue Jan 23, 2018 1:08 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Heat Capacities of Gas
Replies: 1
Views: 75

### Heat Capacities of Gas

When and why do we use the equations in the table on page 281? I get that the molar heat capacity depends on the complexity of the molecule, but I don't think I'm really clear on what situations we would be first expected to use these equations before then solving q = n x C x delta T.
Mon Jan 22, 2018 8:07 pm
Forum: Calculating Work of Expansion
Topic: 8.117 Homework Problem
Replies: 1
Views: 74

### Re: 8.117 Homework Problem

The problem asks about the production of 1.00 mol of H2. If we are only producing 1.00 mol of H2, then we will also only produce 1/3 mol of CO2, and use 1/3 mol of CH4 and 1/3 mol of H2O as reactants (when we use the balanced equation given to us in the problem). When we solve for the net production...
Sat Jan 20, 2018 1:10 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Chapter 8 #99
Replies: 1
Views: 86

### Chapter 8 #99

For 8.99, in order to find the final temperature, we first need to find the enthalpy of reaction. I know that we can find this by using enthalpies of formation of the products and reactants. However, when I calculate it (products - reactants), I get 153.89 kJ/mol, but it should be -153.89 kJ/mol. Wh...
Wed Jan 17, 2018 8:44 pm
Forum: Phase Changes & Related Calculations
Topic: Compression (Question 8.3)
Replies: 4
Views: 126

### Re: Compression (Question 8.3)

Since the work is done on the air (which is our system), the work is positive. The air in the pump is compressed.
Tue Jan 16, 2018 7:51 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Calorimetry
Replies: 2
Views: 147

### Re: Calorimetry

For 8.21, we know that the heat lost by the piece of metal is transferred to the water, so the water gains heat. You would set up the equation by setting the heat lost by the copper = - heat gained by water. You would then use the equation q = mass x specific heat capacity x change in temperature fo...
Thu Jan 11, 2018 6:08 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Book 8.11 [ENDORSED]
Replies: 5
Views: 229

### Re: Book 8.11[ENDORSED]

When we're discussing expansion work, the expansion can either be a reversible or irreversible process. A reversible process can be reversed by an infinitesimal change, and reversible isothermal expansion is expansion at a constant temperature where the external pressure matches the pressure of the ...
Wed Jan 10, 2018 8:39 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Equipartition Theorem
Replies: 1
Views: 115

### Equipartition Theorem

What is the equipartition theorem saying and when would we use it? I understand it can estimate internal energy (or changes in internal energy) based off of translational and rotational contributions, but I don't understand what this really means.
Wed Jan 10, 2018 7:39 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Notation
Replies: 4
Views: 171

### Re: Notation

I believe it's written in scientific notation in order to show how many sig figs there are. In the question, each value has 3 sig figs, but the final answer written as 490 J shows only 2 sig figs. Writing the answer in scientific notation or writing the answer as 490. J will show the correct number ...

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