Topic 7/17: Equilibrium

Question 1

Define chemical equilibrium.

Answer 1

The state in which the rate of the forward reaction equals the rate of the backward reaction in a closed system

Question 2

Describe the features of the equilibrium state.

Answer 2

1. Equilibrium is dynamic - forward and backward reactions at same rate
2. Closed system - prevents exchange of matter with surroundings
3. Concentration of reactants and products remain constant
4. No change in macroscopic properties e.g. color, density
5. Equilibrium can be reached from either direction

Question 3

Describe Le Chatelier’s principle.

Answer 3

Concentration

• ⬆️ shifts eq to side with fewer moles of solute
• ⬇️ shifts eq to side with more moles of solute

Pressure

• ⬆️ shifts eq to side with fewer moles of gas
• ⬇️ shifts eq to side with more moles of gas

Temperature

• Exothermic (negative enthalpy) favors decrease in temperature
• Endothermic (positive enthalpy) favors increase in temperature

Question 4

Describe the effect of catalysts on the equilibrium constant.

Answer 4

Lowers the activation energy an equal amount for both the forward and reverse reaction, so the eq constant is not affected.

Question 5

Define the reaction quotient (Q).

Answer 5

Q measures the relative amounts of products and reactants present during a reaction at a particular point in time.

Question 6

Describe the relationship between Kc (equilibrium constant) and Q (reaction quotient).

Answer 6

• Kc = Q: Equilibrium
• Kc > Q: Q will increase and produce more products (shifts to the right)
• Kc < Q: Q will decrease and create more reactants (shifts to the left)

Question 7

What are the conditions of equilibrium?

Answer 7

• Gibbs free energy is at a minimum
• Entropy is at a maximum