Write rate law expressions?

Question

2NOCl(g) --> 2NO(g) + Cl2(g)
S2O3^2-(aq) + H^+(aq) --> HSO3^-(aq) + S(s)

(Sulfur initially forms a colloid solution so it can be treated as aqueous.)

(1) Write the rate law expression for the above reactions, assuming these are elementary.

(2) If total pressure in the system is doubled, how will it affect the rate of the reaction in each case?

1. So since these are elementary, I think they're written just like this:

rate = k[NOCl]
rate = k[S2O3^2-][H^+]

2. For gaseous reactions, when pressure increases the rate of reaction increases, so the first one would have an increased rate of reaction.

I'm not really sure about the second one though. Tell me if I'm thinking about this the right way: since the reaction is aqueous and nothing is gaseous, then pressure will not affect the rate of reaction

?

Answer 1

Write rate law expressions?
2NOCl(g) --> 2NO(g) + Cl2(g)
rate=k[NOCl]^2 based on the Law of Mass Action. That is not necessarily the actual rate law, which must be determined by experiment.
The effect of pressure depends on how the pressure is increased. IF it is increased by reducing the volume, the side with the smallest number of GAS molecules is favored. In this case the left side will be favored (only 2 gas molecules versus 3 on the right side).
S2O3^2-(aq) + H^+(aq) --> HSO3^-(aq) + S(s)
r=k[2O3^2-][H^+] as you indicated but not necessarily the actual rate law.