Explain how to recognize the conditions under which changes in pressure would affect systems at equilibrium.

Let us explain the conditions under which changes in pressure would affect systems at equilibrium.

• Le Châtelier’s principle - if a system at equilibrium is disturbed, the equilibrium will shift so as to tend to counteract the effect of the disturbance.
• The change in pressure will have a effect only on systems with gases and only if there are different numbers of moles of gas on the reactant and product sides of the equilibrium.
• If the number of moles of gas on product side is higher than on reactant side:

• The increase in pressure will shift equilibrium to the left (reactant side)
• The decrease in pressure will shift equilibrium to the right(product side)
• If the number of moles of gas on reactant side is higher than on product side:

• The increase in pressure will shift equilibrium to the right (product side)
• The decrease in pressure will shift equilibrium to the left(reactant side)
• If the number of moles of gas on reactant side is equal to the number of moles of gas on product side:

The change in pressure will not have an effect on equilibrium.