2SO 2 (g) + O 2 (g) ↔ 2SO 3 (g) ΔH = -395.7kJmol ^ -1 In the equation, an increase in temperature will shift…

Analysis

This question tests your understanding of Le Chatelier’s Principle and the relationship between temperature and the equilibrium constant ($K$) in reversible reactions.

Concept Explanation

1. Le Chatelier’s Principle: This principle states that if a system at equilibrium is subjected to a change in temperature, pressure, or concentration, the system will adjust itself to counteract that change.
2. Effect of Temperature on Equilibrium Position: • The reaction provided is exothermic because the enthalpy change ($\Delta H$) is negative ($-395.7 \text{ kJmol}^{-1}$). • In an exothermic reaction, heat is treated as a "product." • Increasing the temperature adds more heat to the system. According to Le Chatelier’s Principle, the system will shift to the left (the reactant side) to absorb the excess heat.
3. Effect of Temperature on Equilibrium Constant ($K$): • For exothermic reactions, increasing the temperature decreases the value of the equilibrium constant ($K$). • Conversely, for endothermic reactions, increasing the temperature increases the value of $K$.

Step-by-Step Solution

• Step 1: Identify the nature of the reaction. Since $\Delta H$ is negative, the reaction is exothermic.
• Step 2: Determine the shift. Increasing the temperature of an exothermic reaction favors the backward reaction (the reverse direction). Therefore, the equilibrium shifts to the left.
• Step 3: Determine the effect on $K$. Because the reaction is exothermic, an increase in temperature causes the equilibrium constant ($K$) to decrease.

Combining these two findings, an increase in temperature shifts the equilibrium to the left and causes the equilibrium constant to decrease.

Conclusion

The correct option is A.

Exam Tip

Remember the acronym "MEX": More heat (temperature) in an EXothermic reaction shifts the equilibrium to the left (the side of the reactants). Also, always associate "Exothermic" with "Decrease" in $K$ when temperature rises.