Le Chatelier's Principle and ICE Tables

Four disturbances

• Add a substance → shifts away from it. Remove it → shifts toward it.
• Decrease volume (raise pressure) → shifts toward the side with fewer moles of gas. Equal moles on both sides means no shift.
• Change temperature → treat heat as a reactant (endothermic) or product (exothermic). This is the only change that alters $K$.
• Add a catalyst or an inert gas at constant volume → no shift at all.

ICE tables

Rows: Initial, Change, Equilibrium. The change row uses $x$ scaled by the stoichiometric coefficients.

When $K$ is very small, the approximation $[\text{A}]_0-x\approx[\text{A}]_0$ saves solving a quadratic — valid when $x$ is under about $5\%$ of the initial value.