Equilibrium

Question 1

What does equilibrium state?

Answer 1

The rate of the forward reaction EQUALS the rate of the reverse reaction.

(concentrations of reactants and products are constant)

Question 2

What is the relationship between equilibrium and ΔG° (Gibbs free energy)?

Answer 2

When a reaction is in equilibrium the Gibbs free energy of the system is at a minimum.

Question 3

What is the equation for law of mass action?

Answer 3

Question 4

REMEMBER:

In equilibrium expressions, exponents are equal to the coefficients in the balanced equation.

• But DO NOT include solids and liquids into the K_eq expressions.

Answer 4

In rate laws, exponents are NOT equal and must be determined experimentally.

Question 5

What is the equilibrium constant expression for the following reaction?

3 H₂ (g) + N₂ (g) ⇌ 2 NH₃ (g)

Answer 5

The exponents are equal to the coefficients!

Question 6

For the reaction quotient Q, if Q < K_eq, what does that mean?

Answer 6

Q < K_eq

Product favored and the reaction will shift towards the right.

Question 7

For the reaction quotient Q, if Q > K_eq, what does that mean?

Answer 7

Q > K_eq

Reactant favored and the reaction will shift towards the left.

Question 8

For the reaction quotient Q, if Q = K_eq what does that mean?

Answer 8

The reaction is in dynamic equilibrium.

Question 9

What does Le Châtelier’s principle state?

Answer 9

If stress is applied to a system at equilibrium, the system shifts to relieve that stress.

Question 10

For Le Châtelier’s principle, when a reactant or product is added to a system at equilibrium, which direction will the system shift?

Answer 10

AWAY from the added component.

Question 11

For Le Châtelier’s principle, when a reactant or product is removed from a system at equilibrium, which direction will the system shift?

Answer 11

TOWARDS the removed component.

Question 12

For Le Châtelier’s principle, when volume is increased and pressure is decreased in a system at equilibrium, which direction will the system shift?

Answer 12

Towards the side with MORE moles of gas.

(↑volume ↓pressure)

Question 13

For Le Châtelier’s principle, when volume is decreased and pressure is increased in a system at equilibrium, which direction will the system shift?

Answer 13

Towards the side with LESS moles of gas.

(↓volume ↑pressure)

Question 14

For Le Châtelier’s principle, when temperature is increased or decreased in a system at equilibrium, which direction will the system shift?

Answer 14

Heat is treated like a compound.

• Exothermic: heat as a product
• Endothermic: heat as a reactant

Question 15

For Le Châtelier’s principle, what effect would a noble gas (i.e He, Ne etc.) have on a system at equilibrium?

Answer 15

NO EFFECT

Question 16

What is the difference between a reaction under kinetic control or thermodynamic control?

Answer 16

Kinetics: controls the rate of product formation

(at low temperatures)

Thermodynamics: controls the relative stability of products

(at high temperatures)