Kinetics and Equilibria

Question 1

Give Le Chatelier’s Principle.

Answer 1

When a change is applied to a system in dynamic equilibrium, the system reacts in such a way as to oppose the effect of the disturbance.

Question 2

Does Kc change when we change a concentration? Why?

Answer 2

Kc will theoretically be affected, however the constant remains constant at a constant temperature so concentrations shift to keep Kc constant - so the equilibrium position changes but not Kc.

Question 3

What is Kc?

Answer 3

The equilibrium constant - this gives a quantitative value for the position of equilibrium at a given temperature.

Question 4

Give the 6 steps for calculating Kc.

Answer 4

1. Work out the initial moles of each substance (OES).
2. Work out the equilibrium moles OES.
3. Work out the equilibrium concentration OES.
4. Form an expression for Kc.
5. Substitute values into that expression.
6. Find the units for Kc.