The AP Chemistry Study Thread

<p>sorry bud, i wasn't sure if twas "Rate=1.4<em>10^-10" or k=1.4</em>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.</p>

<p>Yeah I think that's k.</p>

<p>Anyway, my calculation went like this</p>

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

<p>and I got NO2 = 0.894 M
Does that seem right?</p>

<p>yeah sounds good.</p>

<p>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?</p>

<p>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.</p>

<p>what is wrong with the Bohr model of the atom?</p>

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

<p>can anyone help me with any of the other questions?</p>

<p>the other ones were right. post a question</p>

<p>Ok </p>

<p>Which of the following does not affect the rate of a reaction?</p>

<p>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)</p>

<p>Btw, what does rxn stand for?</p>

<p>rxn is reaction lol</p>

<p>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...</p>

<p>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!!!</p>

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

<p>if im right....</p>

<p>for the unbalanced gaseous rxn:</p>

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

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

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

<p>Have fun!!!</p>

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

<p>oh gotcha...</p>

<p>I also have this question</p>

<p>Consider the multi-step reaction that has the overall reaction
2A + 2B ---- C + D</p>

<p>What is the rate law expression that would correspond to the following proposed mechanism?</p>

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

<ol>
<li>Rate = k </li>
<li>Rate = k [A]2
2</li>
<li>Rate = k [A]</li>
<li>Rate = k [A]2*</li>
<li>rate = k *
</li>
<li>Rate = k [A]2</li>
<li>Rate = k [A]
</li>
<li>Rate = k [A]
2</li>
<li>Rate = k[A]**</li>
</ol>

<p>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?</p>

<p>quizquick, answer is 5</p>

<p>What is the most massive subatomic particle?</p>

<p>I think the answer to QuizQuick is 8.</p>

<p>The slow step is the rate-determining so:</p>

<p>rate = k ***</p>

<p>But the first equation is equilibrium so:</p>

<p>Keq = * / [A]**
* = Keq [A] **</p>

<p>rate = k Keq [A]** **</p>

<p>and since k*Keq just yields another k.</p>

<p>rate = k [A]**2, or 8.</p>

<p>Let me know if I did something wrong.</p>

<p>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.</p>

<p>Another one is:</p>

<p>For the elementary reaction </p>

<p>CO + O2 ----> CO2 + O</p>

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

<p>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</p>

<p>I put 1, is that right?</p>

<p>Another one is:</p>

<p>For the elementary reaction</p>

<p>CO + O2 ----> CO2 + O</p>

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

<p>rate = k [CO] [O2]</p>

<p>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.</p>

<p>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</p>

<p>My answer would be 2.</p>

<p>Please, someone correct me if I am wrong.</p>

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

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

<p>regarding my question, the most massive subatomic particle is actually an alpha particle.</p>

<p>how do real gases deviate from ideal gases?</p>

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

<p>^ Oh right. That was really stupid of me to read the question wrong...</p>

<p>Real gases deviate from ideal gases because they have intermolecular attractions.</p>

<p>Q: What is a lanthanide contraction?</p>

<p>lanthanide contraction is when the ion radii of the lanthanides is decreasing from 1.061 </p>