[spoudyal3]

Two review questions for AP Chemistry. Both are conceptual and I have done a bit of work on both of them but after all the math questions (buffers and titrations etc) my head kinda hurts a bit and I can not think straight right now. Please help me out!

-Explain each of the following in terms of atomic and molecular structures and/or intermolecular forces
a) Solid K and molten KNO₃ conduct an electric current, whereas solid KNO₃ does not.
b) SbCl₃ has measurable dipole moment, whereas SbCl₅ does not.
c) The normal boiling point of CCl₄ is 77 degrees C, whereas that of CBr₄ is 190 degrees C.
d) NaI(s) is very soluble in water, whereas I₂(s) has a solubility of only .03g per 100 g of water.

Please post a reply to any of these parts even if you do not know the other parts.

This is the mixed thermochem question now.

-The reaction between NO and H₂ is believed to occur in the following three-step process.

NO + NO <--> N₂O₂  (fast)
N₂O₂ + H₂ --> N₂O + H₂O (slow)
N₂O + H₂ --> N₂ + H₂O (fast)

a) Write a balanced equation for the overall reaction.
b) Identify the intermediates in the reaction. Explain your reasoning.
c) From the mechanism represented above, a student correctly deduces that the rate law for the reaction is rate = k[NO]²[H₂]. The student then concludes that (1) the reaction is third-order and (2) the mmechanisminvolves the simultaneous collision of two NO molecules and an H₂ molecule. Are conclusions (1) and (2) correct? Explain.
d) Explain why an increase in temperature increases the rate constant, k, given the rratelaw in (c).

These seemed like classic types of AP questions so I searched previous posts but I was unable to find anything. There is another question that is racking my brain but it involves too much math to be considered purely conceptual. Thanks for any help you can give me.

-DaKid

P.S. How do you make the degree sign? Thanks again.

[Bakegaku]

-Explain each of the following in terms of atomic and molecular structures and/or intermolecular forces
a) Solid K and molten KNO3 conduct an electric current, whereas solid KNO3 does not.

Electrical conductivity is related to the number of mobile charged particles.  Does K has mobile electrons or ions?  are the particles more moveable in KNO₃(s) or KNO₃(l)

c) The normal boiling point of CCl4 is 77 degrees C, whereas that of CBr4 is 190 degrees C.

They have similar structure, and are both nonpolar, so the question is which one is more massive, and which has more electrons to act in the dispersion forces?

d) NaI(s) is very soluble in water, whereas I2(s) has a solubility of only .03g per 100 g of water.

Polar tends to dissolve other polar and ionic substances so the one that is polar or ionic would likely be more soluble than the one that is nonpolar.

[spoudyal3]

Ok, thanks bakegaku. I think I figured out part b now too. Just in case anyone out there does not know, dipole moment is polarity. The the structure of SbCl3 is trigonal pyramidal so it is polar, however, SbCl5 is trigonal bipyramidal so it is nonpolar.

SbCl

             ..
            Sb
          /  |  \ 
       Cl  Cl   Cl

SbCl5

          Cl    Cl
            \   /
      Cl  - Sb -  Cl
              |
             Cl

Can anybody help me out with the first question? Thanks again bakegaku!

-DaKid

P.S. I still have not figured out how to make a degree sign here. Help?

[tamim83]

a) Write a balanced equation for the overall reaction.

Well you know that the reactants are NO and H₂ from the question so now you need to figure out the products.  The products would be those species that seem to be produced but not used up in the reaction mechanism

b) Identify the intermediates in the reaction. Explain your reasoning.

A reaction intermediate is produced but is used up in another part of the reaction.  So you want to look for a species that is produced but is then consumed in another part of the mechanism. 

d) Explain why an increase in temperature increases the rate constant, k, given the reate law in (c).

Think about what happens to the movement of the particles when the temperature is increased.  How would this change impact how quickly ta reaction would increase according to collision theory. 

Hope this helps. 

[spoudyal3]

Hope this helps.  

Definitely! Especially with part d. I would not of thought as far back as collision theory! Thanks for all the *delete me*

-DaKid

[Borek]

P.S. I still have not figured out how to make a degree sign here. Help?

Like this one: ° ?

Character table from your Windows, copy to clipboard and paste.