Equilibrium Study

[chem-nerd]

I'm interested in gathering together some responses to the following equilibrium questions after reading an interesting study (which I will attach after I get responses from a range of people).

Please DO NOT correct anyone's posts. I'm just interested in seeing what people's answers are.

1. if you are a current Unit 3 Chemistry student, either attempt to answer the questions after having a look at the theory (unit 4 content) or, preferably, give it to your chemistry teacher and post their answers.

2. if you have already completed unit 4 and are now studying chemistry at uni, give them a go and maybe even give them to your uni lecturers/tutors and post their responses too.

If you can, also comment on what level of chemistry the person answering has achieved (eg current or past VCE, undergraduate or postgraduate chemistry)

Question 1
The reaction

CS₂(g) + 4H₂(g) ↔ CH₄(g) + 2H₂S(g)

is at equilibrium in a reactor fitted with a movable piston. If a small amount of CS₂(g) is suddenly added to the equilibrium mixture at constant temperature and pressure, what will happen to the number of CH₄(g) molecules when equilibrium is re-established? Give reasons for your answer.

Question 2
The reaction

CO(g) +2H₂(g) ↔ CH₃OH(g)

is at equilibrium in a reactor fitted with a movable piston. What will happen if some argon gas is added to the equilibrium mixture at constant pressure and temperature? Give reasons for your answer.

Question 3
The reaction

N₂O₄(g) ↔ 2NO₂(g)

is at equilibrium in a syringe. If the volume is decreased at constant temperature by moving the plunger, will the concentration of NO₂(g) be higher or lower that the original concentration when equilibrium is re-established? Give reasons for your answer.

[Edmund]

Question 1

The number of molecules will increase. When more reactant () is added, the equilibrium position will shift to the right, thus producing more moles of products, hence the increase.

Question 2

No change. When an inert gas is added, the total pressure increases. However, this does not affect the partial pressures or the concentrations of both the reactants and products. Thus the reaction in equilibrium will remain as it is.

Question 3

The concentration of will be lower. When volume is decreased at constant temperature, overall pressure increases. The equilibrium position will shift left, to the side with fewer moles, to oppose the change. Thus concentration of will decrease.

[Mao]

Clarification needed: does the moveable piston maintain constant pressure?

[chem-nerd]

Clarification needed: does the moveable piston maintain constant pressure?

mmm as far as i'm aware the subjects in the study weren't given this information. i think given the question says it's added at constant P and T that you can assume the piston maintains constant pressure?