CHEMISTRY COMMUNITY

Felicia Fong 2G

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?

Felicia Fong 2G

On Test 2(electrochemistry), number 7 asked to calculate the standard potential for the following reaction using reduction potentials.
Fe3+(aq) + 3e- -> Fe(s)
Was the correct answer= -.037V?

Felicia Fong 2G

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.

Felicia Fong 2G

Example 8.4 in Ch8 and exercise 8.25 use -q=qcal.

Felicia Fong 2G

An adiabatic wall prevents the thermal exchange between the two systems. Diathermic walls allow the thermal exchange.

Felicia Fong 2G

Specific heat capacity is an extensive property because it is always per 1 gram. Enthalpy and entropy are also extensive properties.

Felicia Fong 2G

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?

Felicia Fong 2G

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.

Felicia Fong 2G

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...

Felicia Fong 2G

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.

Felicia Fong 2G

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?

Felicia Fong 2G

Why is n=1? 2H+ + 2e- yields H2. I thought n=2 because of the 2e-

Felicia Fong 2G

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.

Felicia Fong 2G

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.

Felicia Fong 2G

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?

Felicia Fong 2G

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

Felicia Fong 2G

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.

Felicia Fong 2G

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...

Felicia Fong 2G

(a) Cl2(g) + H20(g) yields HCl(aq) + HClO(aq)
Why does the entropy decrease in this reaction?

Felicia Fong 2G

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.

Felicia Fong 2G

Does a negative entropy mean no disorder?

Felicia Fong 2G

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?

Felicia Fong 2G

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.

Felicia Fong 2G

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?

Felicia Fong 2G

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.

Felicia Fong 2G

I believe so. In many problems, 25 degrees C is the standard temperature, if not specifically stated.

Felicia Fong 2G

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...

Felicia Fong 2G

I think expansion work done on a system is positive. Work done by the system would be negative.

Felicia Fong 2G

What is the difference between intensive and extensive properties? Why is it more useful to have intensive properties?

Felicia Fong 2G

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!

Felicia Fong 2G

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?

CHEMISTRY COMMUNITY

Search found 31 matches

Reducing and oxidizing agents

Calculating the standard potential using ∆G=-nFE

Re: state functions

Re: calorimeter examples

Re: adiabatic and diathermic

Re: heat capacity [ENDORSED]

molecularity

Re: Differential vs Integrated [ENDORSED]

Re: Step Speed

Re: Order

Calculating K

14.41

Re: State Functions

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

given two temperatures and 2 volumes solve for delta S

Van't Hoff equation

Re: Homework Problem 9.65

finding heat capacity using q=cΔT

9.33

Re: 9.27 A

negative entropy [ENDORSED]

9.25

Re: Degeneracy

units for delta H

Re: Spontaneous [ENDORSED]

Re: 8.49-temp?

Re: State Functions and Bond Enthalpies

Re: Homework Question 8.47

Intensive vs extensive property

8.55 typo?

Exothermic reaction in bond enthalpy example in lecture