## Search found 31 matches

Sat Mar 17, 2018 4:05 pm
Forum: Balancing Redox Reactions
Topic: Reducing and oxidizing agents
Replies: 1
Views: 180

### Reducing and oxidizing agents

Q: The following redox couple forms a galvanic cell which generates a current under standard conditions.
Pt2+/Pt and AgF/Ag, F-
What is the reducing agent? I know that the AgF/Ag,F- is the oxidation reaction, so it must be Ag or F-. How do you tell which one is the reducing agent?
Sun Mar 11, 2018 4:05 pm
Forum: Work, Gibbs Free Energy, Cell (Redox) Potentials
Topic: Calculating the standard potential using ∆G=-nFE
Replies: 1
Views: 99

### Calculating the standard potential using ∆G=-nFE

On Test 2(electrochemistry), number 7 asked to calculate the standard potential for the following reaction using reduction potentials.
Fe3+(aq) + 3e- -> Fe(s)
Sat Mar 10, 2018 11:23 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: state functions
Replies: 4
Views: 372

### Re: state functions

Heat and work are not state functions because they depend on the path taken as well as the intial and final state. State functions do not depend on the path taken.
Sat Mar 10, 2018 11:18 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: calorimeter examples
Replies: 1
Views: 97

### Re: calorimeter examples

Example 8.4 in Ch8 and exercise 8.25 use -q=qcal.
Sat Mar 10, 2018 11:10 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Replies: 1
Views: 106

An adiabatic wall prevents the thermal exchange between the two systems. Diathermic walls allow the thermal exchange.
Sat Mar 10, 2018 10:59 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: heat capacity [ENDORSED]
Replies: 1
Views: 113

### Re: heat capacity[ENDORSED]

Specific heat capacity is an extensive property because it is always per 1 gram. Enthalpy and entropy are also extensive properties.
Sat Mar 03, 2018 12:09 pm
Forum: Second Order Reactions
Topic: molecularity
Replies: 6
Views: 394

### molecularity

Do you determine the molecularity of a reaction by number of reactants? For example, if NO+NO yields N2O2 then it is bimolecular because there are two reactants?
Sat Mar 03, 2018 12:05 pm
Forum: General Rate Laws
Topic: Differential vs Integrated [ENDORSED]
Replies: 2
Views: 110

### Re: Differential vs Integrated[ENDORSED]

Integrated rate law questions normally give the rate constant and [A]o(initial concentration) and ask you how much remains ([A]t) after a certain amount of time. Or you may be asked to find how long will it take (find t) for concentration to decrease from x mol/L to y mol/L.
Sat Mar 03, 2018 10:32 am
Forum: Reaction Mechanisms, Reaction Profiles
Topic: Step Speed
Replies: 3
Views: 122

### Re: Step Speed

Yes, we may have to determine which step is fast or slow. It is not always given. You can determine the slow step because it will be the only step that matches the rate law. In lecture, the example given was rate=k[NO2] and step 1 was NO2+NO2 yields NO3+ NO. Step 1 matches the rate law because the r...
Sat Feb 24, 2018 10:43 am
Forum: Method of Initial Rates (To Determine n and k)
Topic: Order
Replies: 5
Views: 204

### Re: Order

The order of a reactant is the exponent to which its concentration term in the rate equation is raised. You can find the overall order of the reaction by adding up the orders(powers) of the reactants.
Wed Feb 21, 2018 12:18 pm
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: Calculating K
Replies: 3
Views: 150

### Calculating K

The practice midterm test questions involve calculating K. However, a variety of formulas were used in the solutions. ∆G° = - RT ln K ,
Ecell=(RT/nF) ln K and E=Ecell-.05916V/n * logQ. Does it matter which formula we use?
Mon Feb 19, 2018 11:29 am
Forum: Appications of the Nernst Equation (e.g., Concentration Cells, Non-Standard Cell Potentials, Calculating Equilibrium Constants and pH)
Topic: 14.41
Replies: 1
Views: 100

### 14.41

Why is n=1? 2H+ + 2e- yields H2. I thought n=2 because of the 2e-
Sun Feb 18, 2018 6:28 pm
Forum: Thermodynamic Definitions (isochoric/isometric, isothermal, isobaric)
Topic: State Functions
Replies: 3
Views: 181

### Re: State Functions

Being a state function is important because it means that you can add or subtract. For example, enthalpy is a state function so if you are given the enthalpies for rxn1 and rxn2 you can add them together. Heat is not a state function so you can't simply add and subtract to find q.
Wed Feb 14, 2018 1:49 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: Calculating entropy with changing temperature and volume [ENDORSED]
Replies: 2
Views: 181

### Re: Calculating entropy with changing temperature and volume[ENDORSED]

Do we solve for n using PV=nrt because moles was not given. Also, C was not given to use in the equation with temp change.
Wed Feb 14, 2018 1:16 pm
Forum: Entropy Changes Due to Changes in Volume and Temperature
Topic: given two temperatures and 2 volumes solve for delta S
Replies: 2
Views: 156

### given two temperatures and 2 volumes solve for delta S

Q: A balloon expands from 3.3L at 298K to 9.2x10^5L at 333K. what is deltaS?
To account for the change in volume, I would use deltaS=nRln(V2/V1). How would you account for the temperature change? One equation is deltaS=nCln(T2/T1), but n and C are both unknowns. How would you solve this?
Tue Feb 13, 2018 10:27 pm
Forum: Van't Hoff Equation
Topic: Van't Hoff equation
Replies: 4
Views: 405

### Van't Hoff equation

Because the Van't Hoff equation isn't given on the formula sheet can you use this method?
1. given standard entropy and enthalpy of reaction, solve for delta G using delta(G) = delta(H) - Tdelta(S)
2. Solve for k(equilibrium constant) using delta(G)=-RTlnk
Sun Feb 11, 2018 11:02 pm
Forum: Gibbs Free Energy Concepts and Calculations
Topic: Homework Problem 9.65
Replies: 2
Views: 110

### Re: Homework Problem 9.65

Positive deltaS means the compound is more stable at higher temperatures. Negative deltaS means the compound is less stable at higher temperatures. The free energy of the reaction becomes less favorable as temp increases, only if deltaS is a negative number.
Sat Feb 10, 2018 3:00 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: finding heat capacity using q=cΔT
Replies: 3
Views: 219

### finding heat capacity using q=cΔT

This question is from the 2011 Midterm. Q1a) The enthalpy of combustion of benzoic acid is -3227 kJ/mol. When 1.453g of benzoic acid was burned in a calorimeter, the temp increased by 2.265 degrees C. What is the heat capacity of the calorimeter? The solution is: q=CcalΔT Ccal=-(mol benzoic acid)(-3...
Tue Feb 06, 2018 7:43 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.33
Replies: 1
Views: 77

### 9.33

(a) Cl2(g) + H20(g) yields HCl(aq) + HClO(aq)
Why does the entropy decrease in this reaction?
Sun Feb 04, 2018 12:57 pm
Forum: Calculating Standard Reaction Entropies (e.g. , Using Standard Molar Entropies)
Topic: 9.27 A
Replies: 5
Views: 220

### Re: 9.27 A

Bromine is farther down the periodic table than Flourine. Thus, Bromine is larger and contains more elementary particles than F in HF. More particles means more entropy. To compare entropies, look at the states of matter if they are different. Entropy increases from solid to liquid to gas.
Sun Feb 04, 2018 12:32 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: negative entropy [ENDORSED]
Replies: 10
Views: 343

### negative entropy[ENDORSED]

Does a negative entropy mean no disorder?
Sun Feb 04, 2018 12:27 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: 9.25
Replies: 5
Views: 192

### 9.25

Q:What is the residual molar entropy of SO2F2?
I drew out the 6 different lewis structures for the SO2F2. The formula used is S=klnW. In the solutions manual, it says S=kln6^6.02x10^-23. Why is 6 raised to avogadro's number?
Sat Jan 27, 2018 8:32 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Degeneracy
Replies: 3
Views: 124

### Re: Degeneracy

In the first lecture about entropy we calculated W(degeneracy) in this problem: Two atoms(A,B) in a flask with two equivalent(same energy) states L and R.
We drew the 4 different microstates. The equation we used is W=2^N.
Sat Jan 27, 2018 8:24 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: units for delta H
Replies: 4
Views: 198

### units for delta H

What are the units for delta H when calculating using bond enthalpies? And using standard enthalpies of formation? Is it KJ/mol or just KJ?
Sat Jan 27, 2018 8:20 pm
Forum: Concepts & Calculations Using Second Law of Thermodynamics
Topic: Spontaneous [ENDORSED]
Replies: 6
Views: 202

### Re: Spontaneous[ENDORSED]

An example for a spontaneous process would be a ball falling down a hill. This occurs naturally. A non spontaneous process would be a ball rolling uphill, which wouldn't occur on its own.
Sun Jan 21, 2018 9:04 am
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: 8.49-temp?
Replies: 1
Views: 78

### Re: 8.49-temp?

I believe so. In many problems, 25 degrees C is the standard temperature, if not specifically stated.
Sun Jan 21, 2018 8:57 am
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: State Functions and Bond Enthalpies
Replies: 2
Views: 92

### Re: State Functions and Bond Enthalpies

A state property is a value that is determined by its current state and is not dependent on the path taken to obtain that state. You can determine the change in enthalpy by calculating final - initial. So, you only need the enthalpy of the product and the enthalpy of the reactant to find the enthalp...
Thu Jan 18, 2018 5:11 pm
Forum: Concepts & Calculations Using First Law of Thermodynamics
Topic: Homework Question 8.47
Replies: 4
Views: 168

### Re: Homework Question 8.47

I think expansion work done on a system is positive. Work done by the system would be negative.
Fri Jan 12, 2018 10:40 pm
Forum: Heat Capacities, Calorimeters & Calorimetry Calculations
Topic: Intensive vs extensive property
Replies: 3
Views: 136

### Intensive vs extensive property

What is the difference between intensive and extensive properties? Why is it more useful to have intensive properties?
Wed Jan 10, 2018 4:28 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: 8.55 typo?
Replies: 2
Views: 89

### 8.55 typo?

The second given reaction is 2 Al + O2 → Al2O3. Is it supposed to be 3/2 O2? Without the 3/2 O2, the oxygens do not cancel out. Or am I missing a step? Thanks for the help!
Wed Jan 10, 2018 3:21 pm
Forum: Reaction Enthalpies (e.g., Using Hess’s Law, Bond Enthalpies, Standard Enthalpies of Formation)
Topic: Exothermic reaction in bond enthalpy example in lecture
Replies: 5
Views: 185

### Exothermic reaction in bond enthalpy example in lecture

In the lecture today, we did an example about bond enthalpies. CH2=CH2 + H-Br → CH3-CH2Br. The change in enthalpy of the reaction was -58 KJ. Why is this an exothermic reaction?