Concept preview

What you will be able to do

1. 01Predict shifts caused by volume and pressure changes
2. 02Predict shifts caused by temperature changes
3. 03State which disturbance changes Keq and explain why

For reactions involving gases, the volume of the container is a lever on the equilibrium, because changing the volume changes the pressure and the concentrations of all the gases at once. Decreasing the volume raises the pressure; by Le Châtelier's principle the system responds by shifting toward the side that has fewer moles of gas, because fewer gas molecules exert less pressure and so relieve the disturbance. Increasing the volume lowers the pressure, and the system shifts toward the side with more moles of gas.