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Which of the following changes will shift the reaction in a forward direction?I2(g) ⇌ 2I(g) ∆H° = -150KJ

Correct answer: D. Decrease in temperature

  • A. increase in concentration of I
  • B. increase in total pressure
  • C. decrease in concentration of I2
  • D. Decrease in temperature

Explanation

If the reaction is I2(g) ⇌ 2I(g) with a negative enthalpy change (∆H° = -150 kJ), the forward reaction is exothermic. According to Le Chatelier's principle, the reaction will shift towards the side with fewer moles of gas, or the side with a lower value of Kc, if the temperature is decreased, the pressure is increased, or the concentration of the reactants is decreased. Conversely, the reaction will shift towards the side with more moles of gas, or the side with a higher value of Kc, if the temperature is increased, the pressure is decreased, or the concentration of the reactants is increased. Therefore, to shift the reaction in the forward direction, we can increase the temperature, decrease the pressure, or decrease the concentration of the products.

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About Chemical Equilibrium

Reversible reactions reach dynamic equilibrium when forward and reverse rates become equal, and Le Chatelier's principle predicts the effect of changing concentration, pressure or temperature. The chapter also covers solubility product, the common ion effect, buffer action and the conditions used in Haber's process, with equilibrium shifts distinguished from changes in the equilibrium constant.

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