The AP Chemistry Study Thread

<p>jeez this thread took off.
nice questions guys..... but try and actually answer a question before you post one..... there seems to be MANY questions flying around right now.</p>

<p>if no one objects, if we can remove all previously posted questions (w/out answers) other than oboesmrtguy40's latest in post #54 and QuizQuick's in post #53. QuizQuick, I saw you had many other questions, please post them again one at a time to reduce confusion.</p>

<p>alright, now to answering some of these. QuizQuick- your question</p>

<p>b)particle size is the one that is left after Process of Elimination.
temperature affects, along w/ concentration, catalyst, and removing some of the products (chartiers principle)</p>

<p>smrtguy40- not exactly sure, but I think its E.
my reasoning follows</p>

<p>Pb+2 + 2Cl- --> PbCl2</p>

<p>3 moles of reactant. 1 mole of product.
reaction is spontaneous, therefore statement E is false.</p>

<p>hm... i think particle size will affect the reaction rate - the more surface area, the more collisions (collision theory) that will result in reaction. frankly, i think all the choices can affect reaction rate. do you have the "official" answer?</p>

<p>B The entropy of the universe is increasing...thats the answer...it said which is true, not false. but u would have been right</p>

<p>bah. i need to learn to read.
my bad.</p>

<p>i think i'm still right on quiz quick's though.....</p>

<p>Nope, it's definitely not particle size. I'm taking a computerized take home test and I got that question wrong.</p>

<p>maybe its b? maybe the question is asking for the rate..... like kinetics. cause then, if its 1st order, the concentration doesn't matter...... idk.</p>

<p>Four of the following factors can affect the forward rate of a chemical reaction.
Which one cannot affect this rate?
1) temperature
2) particle size of solid reactants
3) concentration of reactants
4) presence of a catalyst
5) removal of some of the products</p>

<p>Maybe the answer is 5?</p>

<p>..... i guess the rate.... maybe. but le chattiers says that if you remove products the reaction shifts to the right.........
it seems like all of them affect.... idk. i'm way confused on this question.</p>

<p>Possibly, the reaction is not in equilibrium?</p>

<p>Now that I read it again, I think it’s 5. The question says “forward” rate, so why should how much products you have matter if it’s not in equilibrium?</p>

<p>I am reading my AP book about rate and it says that ONLY the species of a reaction AND temperature can affect the rate.</p>

<p>Is the question maybe flawed? I'm not sure.</p>

<p>I suck at equilibrium and I have a question:
If you have a reaction like A->B+C and you are given GRAMS of A, LITERS of rigid container it is put in. It is heated it says at ___ K and it lastly gives the MOLES of C at equilibrium.</p>

<p>Then it asks for the equilibrium concentration of gas A and gas B (all 3 are gases btw)...is this what you would do?...i think im wrong but jw...</p>

<p>divide moles of C by liters to get molarity ?...then make an ice chart where you see that x= Molarity C?. For A you can convert Grams-->Moles then divide by L for Molarity. Then you will have Initial M - x = final. And from C you will have x. </p>

<p>If you know how to do it, ignore these last 2 paragraphs and just post lol because i think i am wrong...or maybe I'm right.</p>

<p>i think its more complex than that due to the heating since temp changes equilibrium constant. don't know how to do it though</p>

<p>Four of the following factors can affect the forward rate of a chemical reaction.
Which one cannot affect this rate?
1) temperature
2) particle size of solid reactants
3) concentration of reactants
4) presence of a catalyst
5) removal of some of the products</p>

<p>OK, I did this question through the process of elimination.
A) temperature~ if you increase the temperature in an exothermic process the reaction will turn left. vice versas for an endothermic system. Thereforem it affects equilibrium.
B) I will get to this later
C) Concentration of reactants~ It matters a whole lot. eg.
X+Y--> XY
lets say you have 100 atm of XY and O atm of X and 300 atm of Y. This system will go toward the reactants to try to produce some X.
D) presence of a catalyst-- it affects the rate of a reaction as we all know by lowering the activation energy of the system.
E) Removal of some products. eg.
XY+Z-->XZ+Y
Lets say you take away some Y from the products. The system will shift left to produce some Y again. </p>

<p>So my answer in B). I am quite sure but if I am wrong please correct me. I want to learn :)</p>

<p>My question (sample AP)</p>

<p>Match the following with the statements given below. An answer can be used more than once or not at all</p>

<p>A) H2
B) He
C) O2
D) N2
E) CO2</p>

<p>(the 2s are subscripts)</p>

<ol>
<li><p>This is the most plentiful gas in the earth atmosphere. (Kudos to those who can say what percent of the atmosphere it makes up)</p></li>
<li><p>A 1 mole sample of this gas occupying 1 liter will have the greatest density</p></li>
<li><p>At a given temperature, this gas will have the greatest effusion. </p></li>
<li><p>The molecules of this gas contain plar bonds</p></li>
<li><p>The molecules of this gas contains triple bonds. </p></li>
</ol>

<p>Good Luck!</p>

<ol>
<li>N2...80%</li>
<li>CO2...NOT SURE</li>
<li>He</li>
<li>O2...NOT SURE</li>
<li>N2 </li>
</ol>

<p>2 and 4 not sure about. please correct me.
My question is posted few posts above.</p>

<p>Sorry if an incomplete message was posted 2ice by me. I pressed reply accidentaly and not sure if I pressed stop quick enough.</p>

<p>Tryingmybest~I think we need more information to solve the problem. If you got the problem from like an AP test, review book, etc. can you please give us exact question. I am completely stumped. </p>

<p>Answers to my question:
1) You are right
2) You are right
3) No
4)No
5) You are right</p>

<p>Anybody else?</p>

<p>1) i think N2 occupies 78%
3) H2
4) if the word "plar" is supposed to be "polar", then none</p>

<p>predicted the following reactions (2000 AP FRQ)
a) a small piece of calcium metal is added to hot distilled water.
e) a solution of tin(II) nitrate is added to a solution of sodium sulfide.
g) powdered strontium oxide is added to distilled water.</p>

<p>for the desity part. is it at ATP? if not, then i don't think it can be solved.</p>

<p>sristi
3) is H2
4) is CO2- the bonds between and C and O are the only bonds I could assume to be polar.</p>

<p>stanfordream, these are all net ionics (which I'm assuming where you are getting these from), I also balanced them, which is not necessary for net ionics
-2Ca + 4H2O --> 2Ca(OH)2 + 2H2
-Sn+2 + S-2 --> SnS
-Sr2O + H2O --> 2Sr+ + 2OH-</p>

<p>Since there's supposed be a lot of equilibrium on the test, here's one:</p>

<p>Calculate the pH at the equivalence point in the titration of 50 mL of .10 M methylamine (CH3NH2) with a .20M HCl.</p>

<p>Kb of CH3NH2 (methylamine): 4.4<em>10^-4 or Ka of CH3NH3+ : 2.3</em>10^-11</p>

<p>HINT: This is a weak base, strong acid titration, so you need to eventually find the pH for the hydrolysis of CH3NH3+ with ICE charts and approximation.</p>

<p>Stanford dream~ for #4: none of them are "polar" like water. But here you need to chose the best answer. only carbon dioxide has some degree of varying electonegativity. </p>

<h1>2 is H2</h1>

<p>Shanianwang~ can you give the volume of the HCl. I think we need it to find the moles of H</p>