The AP Chemistry Study Thread

[stanfordream]

#3, i got 1.53M. here's how i did it,
Rate=k[NO2]^2
solve for k
second order, so 1/x-1/2=kt
solve for x, x=1.53M
is that right?

what is an activated complex?

[theautumneffect]

an activated complex is the transitional/intermediate structure formed when the reactants are turning into products (during a chemical reaction)


what is the purpose of a salt bridge in a galvanic cell?

3. For the reaction 2NO2 ----> 2NO + O2

Rate = 1.4 * 10^-10 M*s [NO2]2 at 25.0 C.
If 2 mol of NO2 are initially present in a sealed 1.00 liter vessel at 25 C, what is the concentration of NO2 after 140 years?

I got 0.894 M.

stanfordream, for that question, doesn't it already tell you k (1.4 * 10^-10?). Also, it doesn't tell you the concentration of NO2, so how can you solve for k?

[smder99]

how do u quote like that (totally unrelated)???




and the ^ question ^.........a saltbridge allows the medium to be more conductive...and the salt used should ionize 100% while not inferring with the redox ur trying to do...(for example... CuCl2 is a bad idea for a salt bridge...go with NaNO3 or the like)



next question:

Briefly describe a laboratory procedure to do the following:

(a) Separate a mixture of powdered solid CaCl2 and CaCO3.

(b) Determine the concentration of NaCl in an aqueous NaCl solution.

(c) Separate a mixture of two volatile liquids.

[celebrian25]

How to quote:

[ quote]what you want quoted[/quote]

remove first space

[stanfordream]

sorry bud, i wasn't sure if twas "Rate=1.4*10^-10" or k=1.4*10^-10 because your units were messed up. so i reasoned that it made more sense for "Rate=1.4*10^-10" because that means you just forgot to raise s to the -1 power. also, it says there are 2M of NO2 at the beginning, so if you actually know the rate and [NO2], you can solve for k since it's an elementary reaction.

Yeah I think that's k.

Anyway, my calculation went like this

1/[NO2] - 1 / 2 M = (1.4 * 10^-10 s^-1) (4.17 * 10^9)

and I got NO2 = 0.894 M
Does that seem right?

[stanfordream]

yeah sounds good.

for smder's question,
a) mix with water and stir carefully. the CaCO3 should precipitate. once precipitation is complete, filter using filter paper.
b) First measure the volume of the solution. now since we have a volatile and a nonvolatile substance, we use distillation to separate completely. distill the water and what remains is NaCl. measure the mass of NaCl and we can find the concentration.
c) this one i'm not too sure. the only thing i can think of is distillation. however, distillation of two volatile liquids won't be pure, but i guess it'll be close enough. any other way?

about salt bridge ... i thought a salt bridge is just a tube or a porous membrane that allows ions to flow through to balance the charge in the two cells. this way, the redox can occur spontaneously w/o interference.

what is wrong with the Bohr model of the atom?

The Bohn model only works for the hydrogen atom and doesn't really explain the properties of more complex elements.

can anyone help me with any of the other questions?

[stanfordream]

the other ones were right. post a question

Ok

Which of the following does not affect the rate of a reaction?

1) The value of delta H(rxn)
2) The temperature of the reactants
3) The presence of a catalyst
4) The value of E(a)


Btw, what does rxn stand for?

[smder99]

rxn is reaction lol

stanfordream...for my question..for the second one i was actually looking for boiling point depression (and u find molality and convert to molarity using density) but i guess distillation works...and yes for the last one it is distillation...



umm QuizQuick ur question...is trickky...im pretty stumped...i know its not 2 or 3...so either its dH or Ea....but which one!!!

ill go with Ea cuz dH can be used to determine spontaneity.....
(4) does not




if im right....

for the unbalanced gaseous rxn:

N2 + H2 ===> NH3 dG = -33.32 kJ/mol at STP


(a) What is the Kp value at STP???
(b) Determine Kp for each of the following scenarios:

- dump in more N2 so that the new partial pressure is double what it was
- increasing the volume of the container by a factor of 2
- increasing the temp from 0C to 20C


Have fun!!!

But doesn't a high activation energy result in a slower reaction and vice versa?

[smder99]

oh gotcha...