Equilibrium Cheat Sheet

Understanding chemical equilibrium is key to predicting reaction direction and extent. It involves reversible reactions where forward and reverse rates are equal, leading to constant concentrations of reactants and products.

Core Principles

Equilibrium is dynamic, not static.
Forward and reverse reaction rates are equal at equilibrium.
Concentrations of reactants and products remain constant at equilibrium.
Equilibrium can be approached from either direction (reactants or products).
The position of equilibrium can be shifted by changing conditions (Le Chatelier's Principle).

Key Terms

Reversible Reaction: A reaction that can proceed in both the forward and reverse directions.:
Equilibrium: The state where the rate of the forward reaction equals the rate of the reverse reaction.:
Equilibrium Constant (Kc): A ratio of product concentrations to reactant concentrations at equilibrium, raised to their stoichiometric coefficients.:
Le Chatelier's Principle: If a change of condition is applied to a system in equilibrium, the system will shift in a direction that relieves the stress.:
Homogeneous Equilibrium: Equilibrium where all reactants and products are in the same phase.:
Heterogeneous Equilibrium: Equilibrium where reactants and products are in different phases.:

Pro Tips

Use ICE tables (Initial, Change, Equilibrium) to solve equilibrium problems.
The magnitude of Kc indicates the extent of the reaction.
Temperature is the only factor that changes the value of Kc.
For heterogeneous equilibria, the concentrations of pure solids and liquids are considered constant and are omitted from the Kc expression.

Pitfalls to Avoid

Assuming equilibrium means concentrations are equal.
Forgetting to include stoichiometric coefficients in the Kc expression.
Ignoring the effect of temperature on Kc.
Treating concentrations of pure solids and liquids in Kc expressions.
Confusing equilibrium with reaction completion.