CHEMISTRY COMMUNITY

Lexie Baughman 2C

Is Gibbs Free Energy of Formation always zero for pure elements? Like in today's review problem, Cl2 had a Gibbs Free Energy of Formation = 0 - does this apply to any element?

Lexie Baughman 2C

When do you include H+ in the cell diagram? Do you always put it in whenever there are H+ ions in a balanced reduction/oxidation half reaction?

Lexie Baughman 2C

As far as practice problems I've seen/done, they'll have to tell you the slow step in a mechanism, and depending whether the slow step involves an intermediate or not, you'll have to tailor your approach.

Lexie Baughman 2C

You do the problem as you would any other redox reaction problem. Obtain the balanced half reactions, multiply the oxidation and reduction half-reactions by appropriate factors that will result in the same number of electrons present, and then add the half reactions. In this case, Cl2 just happens t...

Lexie Baughman 2C

And, once you solve for the reactant orders, you can solve for the rate constant by choosing a set of values from the table and plugging them in. Once you have the rate constant, you can plug in concentrations given from the table and the rate constant you solved for to find an unknown rate of a rea...

Lexie Baughman 2C

So, your rate law will be k = [A]^n x [B]^m. When given a chart, you have to look at two cases: one where [A] is changing but [B] is constant, and one where [B] is changing and [A] is constant. For whichever concentration is changing, use this formula - rate(2)/rate(1) = ([A(2)]/[A(1)])^n - with val...

Lexie Baughman 2C

First calculate the concentration of A at 3 minutes.
[A(t)] = [A(0)] - (1 mol A/3 mol B) x [B(t)] = .015mol/L - (1/3) x .018 mol/L = .009 mol/L
The rate constant is then determined from the first-order integrated rate law.
k = (ln([A(0)]/[A(t)]) / t = ln (.015/.009) / 3 min = .17 min^-1

Lexie Baughman 2C

The rate-determining step is the slowest step in a reaction mechanism. Because it is the slowest, it determines the rate of the overall reaction. In a reaction with a slow initial step, the rate law will simply be determined by the stoichiometry of the reactants.

Lexie Baughman 2C

In a first order reaction, there will be one reactant present in the rate law. For a second order reaction, you can either have a rate law with one reactant to the second order, or with two reactants both to the first order. I remember it by adding the exponents of all the reactants in the rate law ...

Lexie Baughman 2C

What is the chemical formula of the rusting process? I'm not understanding the book's explanation of it.

Lexie Baughman 2C

Residual entropy is the measure of how many different arrangements a molecule can have. Molar entropy is a measure of a molecule's chaos/disorder.

Lexie Baughman 2C

The purpose of the salt bridge is to maintain charge balance. As the electrons move from the anode to the cathode, electrons move from the cathode back to the anode to keep the flow of electrons constant. It ultimately maintains neutrality.

Lexie Baughman 2C

K is greater than one when there are higher concentrations of products than reactants at equilibrium. If K is equal to 1, the reaction favors neither the products or the reactants, meaning that their concentrations are the same.

Lexie Baughman 2C

Can someone explain why we don't use the Cv for a monatomic ideal gas (3/2R) when calculating the change in entropy that accounts for the temperature change of the system? I have delta S = (3.73 mol)(8.314 J/Kmol)ln(348/323) = 3.48 J/K, which includes R but not the 3/2.

Lexie Baughman 2C

Just confirming - when using the bond enthalpies method, it's the sum of the bonds broken minus the sum of the bonds formed, right? This goes against the sum of products minus the sum of reactants in other forms of the equation, so I wanted to make sure I have it right. Thanks!

Lexie Baughman 2C

I believe you can use them in whichever situation - the variables that are constant in each case are the only thing that differ.

Lexie Baughman 2C

Is the integral that is used to describe "a sum of an infinite number of steps" just a way to obtain the w = -P x change of V equation? If not, in what situation would we use it?

Lexie Baughman 2C

This may be a really simple answer, but can someone explain the fundamental different between reversible and irreversible processes? I don't have it in my notes anywhere and I'm getting caught up on it. Thanks!

Lexie Baughman 2C

This is in reference to the work equation, where w = F x D = P x A x D = P x delta V. How does the third equality come from the second one?

Lexie Baughman 2C

The heat change will be made up of two terms - one term to raise the temperature of the copper and the other to raise the temperature of the water.
q = (300g)(4.18J/Cg)(100C-20C) + (400g)(.38J/Cg)(100C-20C) = 1.12x10^5 J = 1.12x10^2 kJ (with C being Celsius)

Lexie Baughman 2C

I was looking over my notes from Friday's lecture and had written down the diagram with C6H12O6 and 6O2 as reactants/6CO2 and 6H2O as products and H/heat given off increasing, but I don't really remember the context it was given in. Can someone explain?

Lexie Baughman 2C

Does anyone have any tips for figuring out this kind of question, where you're given the delta H of fusion and vaporization and heat capacities and have to match it to a graph? I'm just confused on how the information given is supposed to correlate to regions on the graph. Thanks!

Lexie Baughman 2C

It's because most values are averages from measurements of many different compounds. The only time bond enthalpies are accurate is in the case of diatomic molecules, like N2, O2, or HCl.

Lexie Baughman 2C

The only thing Dr. Lavelle said about accuracy was that using bond enthalpies was the least accurate method because the values found in the table are an average calculated from many different compounds. Because of this, I think the other two methods are preferred and can be used interchangeably.

Lexie Baughman 2C

For those who took 14A with Lavelle, is it encouraged to memorize different strong/weak acids and bases for the tests, or is it made known in the question? I just didn't have him last quarter so I'm not sure how much is given to us. Thanks!

Lexie Baughman 2C

My question is in regards to Part B, where it asks the mass of solid Na2O added to the original flask. I'm not understanding why you need to multiply by the molar ratio, 1 mol Na2O/2 mol NaOH, if we're just finding the mass of Na2O. Thanks for the help!

Lexie Baughman 2C

Do we still have homework due the day of the test?

Lexie Baughman 2C

I set up my ICE table the same way you did and got the same values for the equilibrium constant equation, but when I plugged it into my calculator, I got 4.983. Is that an option? Maybe it was just a mistake in entering the values into the calculator.

Lexie Baughman 2C

My question is in regards to Part C of this problem, which asks us to use our results from Part A and B to determine which is more thermodynamically stable relative to its atoms at 1000 Kelvin, Cl2 or F2. I found both of the equilibrium concentrations for Cl2 and F2, and the eq. concentration of F2 ...

Lexie Baughman 2C

My roommate is in 20B right now, and her syllabus looks pretty similar to ours. Her class spends some time on reaction stoichiometry, which we did in 14A, but a majority of her content is thermodynamics and chemical equilibria, which is what we are starting right now. I'm sure you'd be totally fine ...

CHEMISTRY COMMUNITY

Search found 30 matches

Gibbs Free Energy of Formation

H+ in Cell Diagram

Re: Rate Determining Step

Re: 6K.3 part d

Re: solving for rates with charts

Re: solving for rates with charts

Re: 7B.9a

Re: Rate Determining Step

Re: first vs. second order

Rusting Process

Re: Difference between Molar Entropy and Standard Residual Entropy

Re: Salt Bridge

Re: K>1

HOTDOG Question 5A

Bond Enthalpies

Re: equations

Work Formula Involving Integral

Reversible vs. Irreversible

Work Formula

Re: 7th Edition, 4A.7

Friday 2/1 Lecture Notes

Question 4C.15 (7th Edition)

Re: Bond Enthaplies

Re: Preferable Method?

Strong/Weak Acids and Bases

Question 6B.11 (7th Edition)

Homework

Re: Module Part 2 Question

Question 5I.13 (7th Edition)

Re: Chem 20A to Chem 14B