The AP Chemistry Study Thread

I also have this question

Consider the multi-step reaction that has the overall reaction
2A + 2B ---- C + D

What is the rate law expression that would correspond to the following proposed mechanism?

A + B <-------> I (fast)
I + B -------> C + X (slow)
X + A --- D (fast)

1. Rate = k [b]
2. Rate = k [A]2[b]2
3. Rate = k [A]
4. Rate = k [A]2[b]
5. rate = k [i][b]
6. Rate = k [A]2
7. Rate = k [A][i][b]
8. Rate = k [A][b]2
9. Rate = k[A][b]

[stanfordream]

smder,
G=RTlnK
-33320=8.31(273)lnK, solve for K
of the three scenarios, only increase in temp changes the Kp (decrease Kp since exothermic). however, i have no idea how to solve for the new Kp. help?

quizquick, answer is 5

What is the most massive subatomic particle?

[mrniceguy]

I think the answer to QuizQuick is 8.

The slow step is the rate-determining so:

rate = k [i][b]

But the first equation is equilibrium so:

Keq = [i] / [A][b]
[i] = Keq [A] [b]

rate = k Keq [A][b] [b]

and since k*Keq just yields another k.

rate = k [A][b]2, or 8.

Let me know if I did something wrong.

Yeah I guess both could work. At first I did put 5, but then I noticed that there wasn't a 5 in the original reaction...so maybe it's 8. I dunno.

Another one is:

For the elementary reaction

CO + O2 ----> CO2 + O

which of the following is correct (in the order: with respect to CO, overall order, units of rate constant)?

1) 1;2; M^-1 s^-1
2) 1;1; M^-1 s^-1
3) 2;0; M^-1 s^-1
4) 1;1;s^-1
5) 0;1;s^-1

I put 1, is that right?

[smder99]

neutron

stanfordream...if im not mistaken..this is how u would find the new Keq at 40C
(btw..in the original problem i meant to write standard state, not STP)



dG= -RT ln Keq
dG= dH - TdS

dH - TdS = -RT ln Keq


-DH/RT - DS/R = ln Keq

now u would find the dH and dS values for the rxn, plug those in, along with R and the new temperature and find Keq at 40C!!!!!

[mrniceguy]

Another one is:

For the elementary reaction

CO + O2 ----> CO2 + O

Since its an elementary reaction, there are no steps/no mechanism. Hence, the [ ] of each reactant is raised to its coefficient.

rate = k [CO] [O2]

Then, to find the units of k. Think of it logically.
rate must be in units of M/s. Both the [ ] have units of M, so M^2. Hence, units of k must be M^-1 s^-1.

1) 1;2; M^-1 s^-1
2) 1;1; M^-1 s^-1
3) 2;0; M^-1 s^-1
4) 1;1;s^-1
5) 0;1;s^-1

My answer would be 2.

Please, someone correct me if I am wrong.

[stanfordream]

yeah the rate law is 8. i went by it too quickly and didnt see twas a rate mechanism.

smder, ok i see. i didnt know i could look up dH and dS, so i thought there was another way to do it.

regarding my question, the most massive subatomic particle is actually an alpha particle.

how do real gases deviate from ideal gases?

[stanfordream]

for the elementary rate reaction question, the overall order is 2. so quizquick was right.

[mrniceguy]

^ Oh right. That was really stupid of me to read the question wrong...

Real gases deviate from ideal gases because they have intermolecular attractions.

Q: What is a lanthanide contraction?

lanthanide contraction is when the ion radii of the lanthanides is decreasing from 1.061 Ångström La3+ to 0.848 Ångström Lu3+ in the lanthanide period

Q

For the multiple step reaction mechanism

Slow NO + Br2 ---> NOBr2
Fast NOBr2 + NO ----> 2 NOBr
Net 2 No + Br2 ----> 2 NOBr

What would be the correct rate law?

[sristi]

For the multiple step reaction mechanism

Slow NO + Br2 ---> NOBr2
Fast NOBr2 + NO ----> 2 NOBr
Net 2 No + Br2 ----> 2 NOBr

What would be the correct rate law?

I am just guessing but here goes. The slow reaction determins the rate so:
Rate=k[NO][Br]
My question:
What is the difference between alkenes, alkanes, and alkynes?
Good Luck!!

Alkanes have single bonds, alkenes have double bonds, and alkynes have triple bonds.

My q.
When color is Ag2CrO4?

[stanfordream]

no idea, but i'm guessing white?

list the following from the least reactive to the most reactive:
Na, Ca, Mg, K, Cs, Zn