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Concentration changes and chemical equilibrium

The rate and extent of chemical change • Reversible reactions and equilibrium

Key concepts

What you'll likely be quizzed about

  • Dynamic equilibrium is established in a closed system when forward and reverse reaction rates are equal, and concentrations of reactants and products remain constant.
  • Continuous microscopic reactions happen in both directions, leading to stable concentrations at equilibrium.\nWhen concentration changes, the balance of rates is disrupted.
  • An increase in a reactant raises the forward rate relative to the reverse, resulting in a net shift towards producing more products until the rates equalize again.

Flashcards

Test your knowledge with interactive flashcards

What effect does adding an inert gas at constant volume have?

Click to reveal answer

Adding an inert gas at constant volume does not affect the partial pressures of reactive gases, and therefore does not shift the equilibrium.

Key notes

Important points to keep in mind

Always hold temperature constant when comparing Q with Kc.

Calculate Q using current concentrations; compare numerically with Kc to predict direction.

Le Chatelier’s principle indicates direction of shifts for concentration changes.

Catalysts hasten equilibrium attainment but do not affect equilibrium composition.

Pressure changes influence gaseous equilibria according to mole differences.

Use ICE tables to calculate new equilibrium concentrations when needed.

Accurately apply stoichiometric coefficients as exponents in Q and Kc equations.

Open systems disrupt the equilibrium predictions based on Kc due to matter exchange.

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