<p>Thank you for all your explanations.</p>
<p>@orangefroot:
It’s polar because it has the N on the left.</p>
<p>ender94: 13. Evaporation is liquid to gas, so it needs heat to evaporate (delta H is positive), and also changing liquid form to gaseous form means the entropy is gonna increase so delta S is positive. </p>
<ol>
<li>Combustion is burning which means heat’s been given off. So delta H is negative, but once again liquid to gas means entropy is increased so delta S is positive.</li>
</ol>
<p>@ender</p>
<h1>13 has a phase change from l to g so entropy will go up (>0). Evaporation would mean heat is a reactant (H>0).</h1>
<h1>14 is a combustion reaction - heat is a product (H<0). There is a phase change from l to g, so entropy will go up (>0).</h1>
<p>lol I’m too slow =P</p>
<p>thanks feedback and 4khaos. I was thinking that those had to be true for the reaction to occur in the first place (ie dH - and dS + meaning it was always spontaneous or something). Now is makes so much more sense</p>
<p>Why does HCl as pure liquid have dipole dipole interactions? Isn’t it an ionic bond?</p>
<p>^ Doesn’t it have to do with electronegativity differences? Dipole dipole means polar so the differences in electronegativity needs to be around 0.5 - 2 for it to be a polar covalent bond, and over 2.0 to be an ionic bond. The electronegativity difference between H and Cl is too small to be an ionic bond. </p>
<p>I’m confused on boiling points and melting points. On Princeton, it said boiling depends on the number of molecules, so the higher the number of molecules, the higher the boiling point? Does molecular weight have nothing to do with this?</p>
<p>feedback- there are certain trends. For instance boiling pt goes up going down the halogens because the halogens are diatomic and the only forces they have are london dispersion. The greater the molecular weight, the stronger the london forces. So yes, molecular weight does have a little to do with it. Then there is also the trend going down the alkali metals where the boiling pt goes down going down the column.</p>
<p>I always used to think acids were necessarily ionic, but it’s not the case. HCl is a covalent molecule and it has d-d interaction because Cl is electronegative compared to H. Further, it’s in liquid state meaning intermolecular forces are holding it together in liquid state.</p>
<p>Can someone explain 59 on the 2008 mc?</p>
<ol>
<li>count the how many of each gases are in the box. 3 N2O2 & 6 NO2 so if you plug them into the equilibrium constant expression (K=[N2O2] / [NO2]^2) you get 1/2 which is B.</li>
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<p>Going to bed guys . . . good night.
Thanks for all of your help.</p>
<p>Good luck to all!
I hope we all get our desired 5s!
(:</p>
<p>You know what sucks? Your mind not letting you sleep over a test you’re sure you’ll do fine on… I guess I’ll study some more then… fun.</p>
<p>thanks. I was thinking if k>1 then the reaction favors the products, k=1 then it is at equilibrium, and if k<1 then the reaction favors the products. Based on that it should be c which is what I got. I now see how B is correct but what was I thinking of where this is the case?</p>
<p>Anyone know what the possibility of complex ion equilibria being the first FRQ?</p>
<p>Guys,
What do you NOT multiply coefficients by?
Like, enthalpies you multiply . . . Ecells, you don’t?
Anything else?</p>
<p>What would a complex ion equilibria even mean? . . . like Kc or what?</p>
<p>I do not know how they can make complex ions into a problem suitable for the first question so I doubt it. It would most likely be on the MC or the equations.</p>
<p>@abrayo- Ecells are the only one i can think of
complex ions are with ligands. For example something like Zn+2 plus NH3 goes to Zn(NH3)4 +2</p>
<p>Can anyone explain to me the differences between electrolytic cells and galvanic (voltaic) cells?</p>
<p>electrolytic cells require electricity (hence the name) to power it. so it’s nonspontaneous unless you have that jolt of electricity. thus the Ecell is negative.</p>
<p>galvanic cells are the opposite - they run spontaneously 
Ecell is positive.</p>
<p>k, i’m going to bed. g’luck everyone. i’ll probably be sobbing after taking the test tomorrow. let’s just hope the curve doesn’t go up more than 2%.</p>
<p>Okay, now it’s my turn to ask questions.
I just took the 1999 and these are the 3 I need help with.
<a href=“Supporting Students from Day One to Exam Day – AP Central | College Board”>Supporting Students from Day One to Exam Day – AP Central | College Board;
<ol>
<li><p>Which of the following occurs when excess concentrated NH3(aq) is mixed thoroughly with 0.1 M Cu(NO3)2(aq)?
(A) A dark red precipitate forms and settles out.
(B) Separate layers of immiscible liquids form with a blue layer on top.
(C) The color of the solution turns from light blue to dark blue.
(D) Bubbles of ammonia gas form.
(E) The pH of the solution decreases.
(it says the answer is C)</p></li>
<li><p>What is the final concentration of barium ions, [Ba2+], in solution when 100. mL of 0.10 M BaCl2(aq) is mixed with 100. mL of 0.050 M H2SO4(aq)?
(A) 0.00 M (B) 0.012 M
(C) 0.025 M (D) 0.075 M
(E) 0.10 M
(It says it’s C, but what reaction causes the decrease?)</p></li>
<li><p>Which of the following pairs of liquids forms the solution that is most ideal (most closely follows Raoult’s law)?
(A) C8H18(l) and H2O(l)
(B) CH3CH2CH2OH(l) and H2O(l)
(C) CH3CH2CH2OH(l) and C8H18(l)
(D) C6H14(l) and C8H18(l)
(E) H2SO4(l) and H2O(l)
(Apparently it’s D, but I just completely forgot what this means… help?)</p></li>
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