How Does Volume Change Affect Equilibrium in Gas Reactions?

[dolpho]

Homework Statement

Hi there, I'm kinda confused about these two problems.

An equilibrium mixture of NO(g), O2 (g) and NO2 (g) is allowed to expand from 1.0 to 2.0 L at a constant temperature. Given that

2 NO (g) + O2 (g) ---> 2 NO2 (g) which of the following statements is correct?

(A) The concentrations of all three gases are unchanged.
(B) The value of KP would decrease.
(C) The number of moles of NO2 would increase.
(D) The number of moles of O2 would increase.
(E) The number of moles of all three gases are unchanged.

Well since the volume increases, the pressure decreases. And since the reaction wants to increase the pressure again it would make more moles of gas. Meaning it would favor the left side and make more reactants.

I get that sort of, but then I came across this question...

The following RXN is allowed to reach equilibrium in a glass bulb at a given temp.
2 HgO (solid) <---> 2 Hg (liquid) + O2 (gas) The mass of the Hg in the bulb can be increased by?

So I thought since we want a reaction that favors the solid, we could decrease the volume, which increases the pressure. The reaction would then make less moles of gas, which would increase the reactant's mass...

But the answer is *increase the volume of the bulb*? I'm not really sure how they came to that conclusion and would appreciate any help!

 

[epenguin]

Homework Statement

Hi there, I'm kinda confused about these two problems.

An equilibrium mixture of NO(g), O2 (g) and NO2 (g) is allowed to expand from 1.0 to 2.0 L at a constant temperature. Given that

2 NO (g) + O2 (g) ---> 2 NO2 (g) which of the following statements is correct?

(A) The concentrations of all three gases are unchanged.
(B) The value of KP would decrease.
(C) The number of moles of NO2 would increase.
(D) The number of moles of O2 would increase.
(E) The number of moles of all three gases are unchanged.

Well since the volume increases, the pressure decreases. And since the reaction wants to increase the pressure again it would make more moles of gas. Meaning it would favor the left side and make more reactants.

I get that sort of, but then I came across this question...

The following RXN is allowed to reach equilibrium in a glass bulb at a given temp.
2 HgO (solid) <---> 2 Hg (liquid) + O2 (gas) The mass of the Hg in the bulb can be increased by?

So I thought since we want a reaction that favors the solid, we could decrease the volume, which increases the pressure. The reaction would then make less moles of gas, which would increase the reactant's mass...

But the answer is *increase the volume of the bulb*? I'm not really sure how they came to that conclusion and would appreciate any help!

It seems your reasoning is OK and that you have just misread or something - you do not want to favour the solid, Hg is liquid.