HW 2 - 13.4 Le Chatelier's Principle Concentration and Pressure Changes

Changes in pressure have a measurable effect: (select all that apply)

- only in systems in which gases are involved - only when the chemical reaction produces a change in the total number of gas molecules in the system

What is the summary of Le Chatelier's Principle?

A chemical equilibrium, when exposed a stress, will shift so as to regain equilibrium.

Consider the reaction described by the following equation. CO₂(g) + H₂(g) ⇌ CO(g) + H₂O (g) How will the position of the equilibrium change if the volume of a vessel that contains this reaction is decreased?

No change will be observed. (A decrease in the volume of the reaction vessel will cause the pressure to increase; however, this will have no effect on the position of the equilibrium. This is because the reaction does not result in a change in the number of moles of gas.)

Which will cause the following equilibrium to shift to the right? 2H₂(g) + S₂ ⇌ 2H₂S(g)

a decrease in the volume of the vessel in which the reaction is contained

What will be the result if the volume of a vessel that contains this reaction is decreased? PCl₃ (g) + Cl₂ (g) →PCl₅ (g) a. The pressure will increase and the equilibrium will shift toward products. b. The pressure will increase and the equilibrium will shift toward reactants. c. The pressure will increase but no change will occur. d. The result is impossible to predict.

a. The pressure will increase and the equilibrium will shift toward products.

What will happen to the following equilibrium if the volume of the reaction vessel increases? 2NO₂ (g) ⇌ N₂O₄ (g) a. it will shift to the left b. it will shift to the right c. there will be no change d. it depends on the factor by which the volume increases.

a. it will shift to the left (If the volume increases, the pressure will decrease, disturbing the equilibrium between the gases. The reaction will shift left (toward the side with more moles of gas) in order to regain some of the lost pressure.)

If the reactants are removed from a system at equilibrium, the equilibrium will: a. shift left b. shift right c. no change d. depends on the equilibrium

a. shift left (equilibrium will shift left to try to regenerate some of the reactants and regain equilibrium)

For the following equilibrium, what will occur if the vessel expands: 2O₃ (g) → 3O₂ (g) a. shift right b. shift left c. no change d. impossible to predict

a. shift right (If the vessel expands, the pressure will drop, and it will shift right to the side with more moles of gas particles to regain some of the lost pressure.)

What will happen to the following equilibrium reaction if the volume of the container in which the gasses are contained decreases? 2NO₂ (g) + O₂ ⇌ 2NO (g) a. shift to the right b. shift to the left c. no change d. it depends on the factor by which the volume decreases

a. shift to the right (If the volume decreases, the pressure will increase, disturbing the equilibrium between the gases. The reaction will shift right (toward the side with fewer moles of gas) to relieve some of the additional pressure.)

A small amount of product is removed from a system at equilibrium. What will change? (choose all the apply) a. the amount of reactants b. the value of Q c. the value of the equilibrium constant d. the temperature associated with the equilibrium constant describing this system

a. the amount of reactants and b. the value of Q

Based on the following equation, if the pressure decreases, the equilibrium will shift: N₂ (g) + 3H₂ (g) ⇌ 2NH₃ (g) a. to the left b. to the right c. depends d. not enough information

a. to the left

Which will cause the following equilibrium to shift to the left? 2SO₂(g) + O₂ ⇌ 2SO₃(g)

an increase in the volume of the vessel in which the reaction is contained (If the vessel's volume increases, the pressure will decrease, disturbing the equilibrium between the gases. The reaction will shift left (toward the side with more moles of gas) in order to regain some of the lost pressure.)

For the following equilibrium, what will occur if the vessel contracts: C (s) + H₂O (g) ⇌ CO (g) + H₂ (g) a. shift right b. shift left c. no change d. impossible to predict

b. shift left (the pressure will increase and the equilibrium will shift to the side with fewer moles of gas. Carbon is a solid in this equation, so it will not count towards moles of gas.)

If more reactants are added to a system at equilibrium, the equilibrium will: a. shift to the left b. shift to the right c. no change d. depends on the equilibrium

b. shift to the right

How will the position of the equilibrium change if the volume of the vessel in which the reaction is contained increases? I₂ (g) + Cl₂ ⇌ 2ICl (g) a. The equilibrium will shift to the left. b. The equilibrium will shift to the right. c. No change will be observed. d. Not enough information given.

c. No change will be observed. (An increase in the volume of the reaction vessel will decrease the partial pressures of the species involved in this reaction. However, this decrease in pressure will not affect the position of the equilibrium because the total amount of gas is unchanged during the course of this reaction; 2mol of reactant produces 2mol of product. Therefore, no change in the equilibrium position will be observed.)

A stress on a system can be considered anything that will alter the: a. identity of reactants or products b. rate of equilibrium c. position of the equilibrium d. none of the above

c. position of the equilibrium

What will happen to the following equilibrium if the volume of the vessel in which the equilibrium is contained increases? 2CH₄ (g) ⇌ C₂H₆ (g) +H₂ (g) a. it will shift to the left b. it will shift to the right c. there will be no change d. it depends on the factor by which the volume increases

c. there will be no change (same number of moles on each side, so no change)

What will NOT change in equilibrium in a reaction involving gases? a. decreasing the volume of the system to one third of its original value b. increasing the volume of the system to three times its original value c. tripling the amount of one of the components in the system d. tripling the amount of all of the components in the system

d. tripling the amount of all of the components in the system (Changing the amount of all of the components does not affect the equilbrium because the relative amounts of each component with respect to that of the others stays the same.)

What has the potential to change the equilibrium in a reaction involving gases? a. decreasing the volume of the system to half its original value b. increasing the volume of the system to twice its original value c. doubling the amount of one of the components in the system d. doubling the amount of all of the components in the system e. all of the above

e. all of the above

A change in pressure will have an effect on:

gaseous equilibria

If a variance in pressure acts as a stress on the equilibrium of a system, which of the following MUST be a part of the system?

gases

For the following equilibrium, what will occur if the vessel contracts: 2NO₂(g)→N₂O₄(g)

shift right (if the vessel contracts, the pressure will increase, and it will shift right to the side with fewer moles of gas particles to alleviate some of the additional pressure.)