CHEMISTRY COMMUNITY

Adrienne Dang 1B

I think in this problem you use K instead of Q because when we are given a pH, we assume that the concentrations are at equilibrium. Basically, if a solution is at a certain pH, the concentrations are not going to change at that temperature.

Adrienne Dang 1B

The big K is the equilibrium constant for step 1, and that is used for this approach since we assume that this step in the reaction is working in equilibrium, as a result of step 2 being the slow reaction. The little k is the rate constant.

Adrienne Dang 1B

If the cell potential is greater than 0, the concentration of the cathode should be greater than the concentration of the anode

Adrienne Dang 1B

If the oxidation number is going from +1 to 0, it is gaining an electron, and doesn't that mean it is being reduced? I thought the reducing agent was the substance that was oxidized?

Adrienne Dang 1B

For question 6B, it asks to identify the reducing agent of a redox couple that forms a galvanic cell. The redox couple is Pt2+/Pt and AgF/Ag,F-
I know that the oxidizing agent is Pt2+ and for the reducing agent I thought it was F- but that answer was incorrect. Can someone explain this to me?

Adrienne Dang 1B

Yes exactly! You should get the same answer for both methods, it just depends on which method you prefer (I personally prefer using Ecell=Ecathode-Eanode just because it's easier for me)

Adrienne Dang 1B

In class we went over the arrhenius equation as being k=Ae^-Ea/RT, with a being the "pre-exponential factor" but in homework problems we never actually use that equation in that form. I've only seen it used in this form: ln (k2/k1)=-Ea/RT(1/T1-1/T2) in order to find the activation energy, ...

Adrienne Dang 1B

You would make a table like the ones that were drawn in lecture. Energy is the y-axis and the progress of the reaction is the x-axis. You would start with the reactants and draw the energy barrier(s) and then end with the products, most often with a lower energy than the reactants

Adrienne Dang 1B

I noticed that the book used the slope of the function in order to calculate the activation energy. Will we have to use a linear regression tool as stated in the textbook or would that information usually be given to us?

Adrienne Dang 1B

I'm pretty sure you are correct with the units. I got L mol-1s-1 as well for the units!

Adrienne Dang 1B

We actually haven't gone over this equation in lecture yet, but you basically just plug in the given k values and temperatures into this equation:
ln (k'/k)=(Ea/R)(1/T-1/T'), and you would just rearrange the equation to get the activation energy.

Adrienne Dang 1B

In lecture, we went over a problem like this but the only reason there was a 2 was because the rate=(1/2)d[NO2]/dt since there is a stoichiometric coefficient of 2 for NO2 in the given reaction. Therefore, to get d[NO2]/dt by itself we multiplied the other side by 2. That's the only reason I think t...

Adrienne Dang 1B

Why did the acid go to the gym?
To become a buffer solution!

Adrienne Dang 1B

What did the scientist say when he found 2 isotopes of helium? Hehe

Adrienne Dang 1B

Can someone explain to me why you are supposed to divide the units by (mol A)/L for the first-order reaction?

Adrienne Dang 1B

Is the unique rate the same in every reaction whether you use values of the reactants or products?

Adrienne Dang 1B

I know that we discussed in class the difference between using log and ln in the nernst equation, but is there any specific reason we would choose one over the other? or does it not matter?

Adrienne Dang 1B

First you need to write both of the half reactions, the reduction reaction and the oxidation reaction. Each half reaction in this case has a standard potential of 0. So when you plug that into the equation for the standard potential of the cell (subtracting that of the anode from the cathode potenti...

Adrienne Dang 1B

I think it's more important that you just understand galvanic cells in general, and I don't think you need to remember the specifics of the Daniell Cell or other examples, just know how they work

Adrienne Dang 1B

For part c and d of this question, how do we know whether positional or thermal disorder is dominant? I know that in d, the solution manual says that the surroundings participate in the solution process only as a source of heat, so the entropy change of the surroundings is primarily a result of the ...

Adrienne Dang 1B

Is it safe to assume that for any given reaction, if the the number of moles of gas is less on the product side, the entropy should decrease?

Adrienne Dang 1B

For these types of questions, will you always have to figure out the number of different possible orientations of the molecule by drawing it out?

Adrienne Dang 1B

For the third part of the example in the book, How would we know to use Cp,m= 4R? And why didn't they use that value to calculate the step 1 of heating the liquid acetone?

Adrienne Dang 1B

yes, so it is basically defining absolute zero on the entropy scale and this is important because the entropy determined relative to this point is the absolute entropy.

Adrienne Dang 1B

I'm not sure if we've gone over this in class, but I think the principle of minimum energy and the entropy maximum principle should help you understand this concept more! Also, I think referring to entropy as disorder is probably causing more misunderstanding about this topic.

Adrienne Dang 1B

It's basically just saying that the entire internal energy of a system is not all convertible into useful work. The portion that can be converted into useful work can be referred to as the available energy, and the portion that cannot is the unavailable energy. And I believe entropy is the measure o...

Adrienne Dang 1B

R is just the gas constant from the ideal gas law (PV=nRT), so it would be 8.314 J K^-1 mol^-1)

Adrienne Dang 1B

I don't think there's a specific way to determine the standard state of an elements, but it is pretty self explanatory for the most part. For example, the standard state for the noble gases would be gas, for metals and metalloids it would be solid (for the most part), and for halogens it varies, but...

Adrienne Dang 1B

Yes, in general molar heat capacity increases with molecular complexity, because with more complex molecules, there are more possible bond vibrations that can absorb the added energy, making the heat capacity higher for the molecule.

Adrienne Dang 1B

I think it depends on the problem. I do know that delta h f (standard enthalpy of formation) is always in kj/mol. Most delta h values given in tables are in kj/mol, because they don't assume any values in the reaction. However, if the problem specifies mass or moles, you would likely multiply it by ...

CHEMISTRY COMMUNITY

Search found 30 matches

Re: Chapter 14 # 107

Re: Q7b Lyndon's Review

Re: Cell Diagrams for Concentration Cells

Re: Test 2 Q6

Test 2 Q6

Re: Calculating Standard Cell Potential

Arrhenius Equation

Re: Drawing Reaction Profiles

Example 15.8 [ENDORSED]

Re: 15.63 units and reaction order

Re: 15.61

Re: Self Test 15.11B

Re: Post All Chemistry Jokes Here

Re: Post All Chemistry Jokes Here

15.9b

Re: Unique Rate [ENDORSED]

Nernst Equation (log vs. ln)

Re: 14.37

Re: The Daniell Cell

9.85

9.33

9.25

Re: 9.19

Re: Third Law of Thermodynamics

Re: More Entropy vs. Less Entropy

Re: Question About Entropy

Re: Formula for reversible expansion

Re: Standard State

Re: problem 8.29

Re: Delta values