Equilibrium Problems and LeChatelier's Principle

Question 1

For 2HI ⇌ H2 + I2, if [H2] changes by x, by what factor does [HI] change?

Answer 1

-2x
(stoichiometric coefficients)

Question 2

Small x approximation only works if what condition is satisfied?

Answer 2

When [Change]/[Initial] is less than 5% for each species in the reaction

Question 3

Does small x approximation work better when K is very large or very small?

Answer 3

When K is very small

Question 4

Will adding more of a reactant change the equilibrium concentrations of a reaction?

Answer 4

Yes

Question 5

Will adding more of a reactant change the K of a reaction?

Answer 5

No

Question 6

Le Chatelier’s Principle: What happens when a system at equilibrium is disturbed?

Answer 6

It regains equilibrium through a reaction that counters the disturbance

Question 7

2H2S (g) + O2 (g) ⇌ 2S (s) + 2H2O (g)
At equilibrium, if [H2S] and [O2], increase, in what direction does the reaction shift?

Answer 7

To the right. Corresponding increase in products to restore equilibrium

Question 8

2H2S (g) + O2 (g) ⇌ 2S (s) + 2H2O (g)
At equilibrium, if [H2S] is removed, does [O2] increase or decrease?

Answer 8

Increases. The reaction shifts to the left to restore equilibrium, making more H2S and O2.

Question 9

2H2S (g) + O2 (g) ⇌ 2S (s) + 2H2O (g)
At equilibrium, if [H2S] is removed, does [O2] increase or decrease?

Answer 9

Increases. The reaction shifts to the left to restore equilibrium, making more H2S and O2.

Question 10

2H2S (g) + O2 (g) ⇌ 2S (s) + 2H2O (g)
At equilibrium, if [S] increases, what happens to [H2S]?

Answer 10

Nothing, stays the same.
Sulfur is a solid, doesn’t factor into Q or K. The system is still at equilibrium.

Question 11

Le Chatelier’s Principle: If the pressure of a system at equilibrium increases and volume decreases, which way does the reaction shift?

Answer 11

Toward the side with fewer moles of gas or solution.

Question 12

H2 (g) + I2 (g) ⇌ 2HI (g)
At equilibrium, pressure increases and volume decreases. Which way does the reaction shift?

Answer 12

No shift. Both sides have 2 moles.

Question 13

2H2S (g) + O2 (g) ⇌ 2S (s) + 2H2O (g)
At equilibrium, pressure increases and volume decreases. Which way does the reaction shift?

Answer 13

Toward the right.
The right has 2 moles of gas
The left has 3 moles of gas

Question 14

In a reaction, the changes in concentration that the species experience to achieve equilibrium are related by what?

Answer 14

The stoichiometric coefficients

Question 15

A change in what condition causes a change in K?

Answer 15

Temperature

Question 16

Does changing the concentration of a chemical species change K?

Answer 16

No

Question 17

If volume increases, does the equilibrium shift to the side with more or less moles of gas?

Answer 17

More moles
Volume increases –> concentration decreases –> system form more moles to restore equilibrium

Question 18

Does a change in pressure/volume change K?

Answer 18

No

Question 19

At equilibrium, does increasing temperature shift the equilibrium toward endothermic or exothermic direction?

Answer 19

Endothermic direction to consume heat

Question 20

At equilibrium, does decreasing temperature shift the equilibrium toward endothermic or exothermic direction?

Answer 20

Exothermic direction to produce heat

Question 21

For an exothermic system, does an increase in temperature increase or decrease K?

Answer 21

Decrease K

Question 22

For an endothermic system, does an increase in temperature increase or decrease K?

Answer 22

Increase K