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Heterogeneous equilibria Knowledge-Based Practice

Chemistry · Chemical Equilibrium · Chemistry · Dynamic Equilibrium

5 Chemistry practice questions on Heterogeneous equilibria. Questions that assess core concepts and understanding.

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Questions

  1. 1.

    A mixture of solid calcium carbonate, solid calcium oxide, and carbon dioxide gas is at dynamic equilibrium in a closed cylinder with a movable piston according to the reaction CaCO3(s)⇌CaO(s)+CO2(g)\text{CaCO}_3(s) \rightleftharpoons \text{CaO}(s) + \text{CO}_2(g). Which statement correctly describes the system after the volume of the cylinder is increased at constant temperature, assuming both solids remain present?

    • A) The equilibrium partial pressure of CO2(g)\text{CO}_2(g) remains unchanged, and the amount of CaO(s)\text{CaO}(s) increases.
    • B) The equilibrium partial pressure of CO2(g)\text{CO}_2(g) decreases by half, and the amount of CaO(s)\text{CaO}(s) remains unchanged.
    • C) The equilibrium partial pressure of CO2(g)\text{CO}_2(g) increases, and the amount of CaCO3(s)\text{CaCO}_3(s) increases.
    • D) The equilibrium partial pressure of CO2(g)\text{CO}_2(g) remains unchanged, and the amount of CaO(s)\text{CaO}(s) decreases.
  2. 2.

    Solid ammonium hydrogen sulfide decomposes according to the heterogeneous equilibrium reaction NH4HS(s)⇌NH3(g)+H2S(g)\text{NH}_4\text{HS}(s) \rightleftharpoons \text{NH}_3(g) + \text{H}_2\text{S}(g). If the total pressure at equilibrium in an evacuated closed container is 0.80 atm at a given temperature, what is the value of KpK_p?

    • A) 0.80
    • B) 0.40
    • C) 0.16
    • D) 0.040
  3. 3.

    In the formulation of equilibrium constant expressions for heterogeneous equilibria, why are pure solids and pure liquids omitted?

    • A) They do not participate in the elementary steps of the forward or reverse reactions.
    • B) Their molar concentrations are intensive properties determined by density and molar mass, remaining constant at a given temperature.
    • C) Their vapor pressures are zero, preventing them from exerting chemical potential in the system.
    • D) Their thermodynamic activities fluctuate unpredictably during the reaction, preventing consistent measurement.
  4. 4.

    Which of the following is the correct equilibrium constant expression (KcK_c) for the heterogeneous reaction SnO2(s)+2CO(g)⇌Sn(s)+2CO2(g)\text{SnO}_2(s) + 2\text{CO}(g) \rightleftharpoons \text{Sn}(s) + 2\text{CO}_2(g)?

    • A) Kc=[Sn][CO2]2[SnO2][CO]2K_c = \frac{[\text{Sn}][\text{CO}_2]^2}{[\text{SnO}_2][\text{CO}]^2}
    • B) Kc=[CO]2[CO2]2K_c = \frac{[\text{CO}]^2}{[\text{CO}_2]^2}
    • C) Kc=[CO2][CO]K_c = \frac{[\text{CO}_2]}{[\text{CO}]}
    • D) Kc=[CO2]2[CO]2K_c = \frac{[\text{CO}_2]^2}{[\text{CO}]^2}
  5. 5.

    Which statement correctly describes the effect of adding an additional amount of a pure solid reactant to a closed system at heterogeneous equilibrium at constant temperature?

    • A) It has no effect on the equilibrium concentrations of the gaseous species because the effective concentration of a pure solid remains constant.
    • B) It shifts the equilibrium toward the products, thereby increasing the concentrations of the gaseous species.
    • C) It increases the numerical value of the equilibrium constant because the total mass of the reactants is increased.
    • D) It shifts the equilibrium toward the reactants, thereby decreasing the partial pressures of the gaseous species.

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