How Does Volume Change Affect Equilibrium in Gas Reactions?

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In summary: The volume of the bulb is proportional to the amount of gas, so increasing the volume of the bulb would decrease the pressure and drive the reaction towards the right, increasing the amount of Hg.In summary, the first problem deals with an equilibrium mixture of gases expanding at a constant temperature. The correct statement is that the number of moles of all three gases is unchanged. In the second problem, the mass of Hg in the bulb can be increased by increasing the volume of the bulb, which decreases the pressure and drives the reaction towards the right, increasing the amount of Hg.
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dolpho
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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!
 
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  • #2
dolpho said:

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.
 

Related to How Does Volume Change Affect Equilibrium in Gas Reactions?

1. What is Le Chatelier's Principle?

Le Chatelier's Principle is a chemical principle that states that when a system at equilibrium is subjected to a change, the system will adjust in a way to counteract the change and maintain equilibrium.

2. Who discovered Le Chatelier's Principle?

Le Chatelier's Principle was discovered by French chemist Henry Louis Le Chatelier in 1884.

3. How does Le Chatelier's Principle apply to chemical reactions?

Le Chatelier's Principle can be applied to chemical reactions by predicting how the system will shift in response to changes in temperature, pressure, or concentration of reactants or products.

4. What factors can affect a system's equilibrium according to Le Chatelier's Principle?

The factors that can affect a system's equilibrium according to Le Chatelier's Principle are temperature, pressure, and concentration of reactants and products.

5. Can Le Chatelier's Principle be used to predict the direction of a reaction?

Yes, Le Chatelier's Principle can be used to predict the direction of a reaction by determining which way the equilibrium will shift in response to a change in one of the factors affecting the system.

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