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Chemical Equilibrium - General Chemistry

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  • What is chemical equilibrium?

    Chemical equilibrium is the state where the forward and reverse reactions occur at the same rate, so concentrations of reactants and products remain constant over time.

  • What does dynamic equilibrium mean?

    Dynamic equilibrium means that reactions continue to occur in both directions simultaneously, but there is no net change in concentrations.

  • How is the equilibrium constant expression written for a reaction \(aA + bB \rightleftharpoons cC + dD\)?

    K = \(\frac{[C]^c[D]^d}{[A]^a[B]^b}\), where concentrations are at equilibrium and raised to their stoichiometric coefficients.

  • What does it mean if the equilibrium constant K > 1?

    The reaction is product-favored at equilibrium, meaning products predominate.

  • What does it mean if 0 < K < 1?

    The reaction is reactant-favored at equilibrium, meaning reactants predominate.

  • How does multiplying a chemical equation by a factor n affect the equilibrium constant?

    The new equilibrium constant is the original constant raised to the power n: K' = Kn.

  • How is the equilibrium constant for a reverse reaction related to the forward reaction?

    The equilibrium constant for the reverse reaction is the reciprocal of the forward reaction constant: Krev = 1 / Kfwd.

  • How do you find the overall equilibrium constant when combining reactions?

    Multiply the equilibrium constants of the individual reactions to get the overall constant.

  • What is the relationship between Kp and Kc for gaseous equilibria?

    Kp = Kc(RT)\(\Delta n\), where \(\Delta n\) is the change in moles of gas (products - reactants).

  • How are pure solids and liquids treated in equilibrium constant expressions?

    Pure solids and liquids are assigned an activity of 1 and do not appear in the equilibrium expression.

  • What is an ICE table used for?

    An ICE table helps track Initial, Change, and Equilibrium concentrations or pressures to calculate equilibrium constants or concentrations.

  • What is the reaction quotient Q?

    Q is the ratio of product to reactant concentrations at any point, not necessarily at equilibrium, used to predict reaction direction.

  • How can you predict the direction of a reaction using Q and K?
    • If Q < K, reaction proceeds forward (forms products).
    • If Q = K, system is at equilibrium.
    • If Q > K, reaction proceeds backward (forms reactants).
  • What is Le Chatelier's Principle?

    When a system at equilibrium is disturbed, it shifts to counteract the disturbance and restore equilibrium.

  • How does adding more reactant affect equilibrium?

    Adding reactant shifts the equilibrium to the right, producing more products.

  • How does increasing the volume of a gaseous reaction vessel affect equilibrium?

    Increasing volume decreases pressure, shifting equilibrium toward the side with more gas molecules.

  • How does decreasing temperature affect an exothermic reaction at equilibrium?

    Decreasing temperature shifts equilibrium to the right (toward products) for exothermic reactions.

  • How does increasing temperature affect an endothermic reaction at equilibrium?

    Increasing temperature shifts equilibrium to the right (toward products) for endothermic reactions.

  • What approximation can be made when K is very small (≤ 10-5)?

    The change in reactant concentration is negligible, so initial concentration ≈ equilibrium concentration.

  • What is the significance of the 5% rule in ICE table approximations?

    If the change x is less than 5% of the initial concentration, the approximation ignoring x is valid.

  • How do you solve for equilibrium concentrations using an ICE table?

    Set initial concentrations, express changes with variable x using stoichiometry, write equilibrium expressions, and solve for x using the equilibrium constant.