What happens to the position of equilibrium, if a reversible exothermic reaction is subjected to a decrease in temperature?

Analysis of the Question

This question tests your understanding of Le Chatelier’s Principle, which states that if a dynamic equilibrium is disturbed by changing the conditions (such as temperature, pressure, or concentration), the position of equilibrium shifts to counteract the change.

Concept Explanation

For a reversible reaction, we look at how heat behaves:

• Exothermic reactions: These reactions release heat. We can think of heat as a product of the reaction. • Equation: $Reactants \rightleftharpoons Products + Heat$
• Le Chatelier’s Principle regarding Temperature: • If you increase the temperature, the system tries to absorb the extra heat by shifting in the endothermic direction (left). • If you decrease the temperature, the system tries to produce more heat to compensate for the loss. It does this by shifting in the exothermic direction (right).

Step-by-Step Solution

1. Identify the reaction type: The question specifies an exothermic reaction.
2. Represent the heat: Since it is exothermic, heat is on the product side.
3. Apply the change: We are decreasing the temperature (removing heat).
4. Predict the shift: According to Le Chatelier’s Principle, the system will attempt to replace the heat that was removed. To produce more heat, the reaction must proceed in the forward direction.
5. Conclusion: The forward direction is the "right" side of the chemical equation. Therefore, the equilibrium position shifts to the right to produce more heat.

Identifying the Answer

Based on the principle explained above, decreasing the temperature of an exothermic reaction favors the forward reaction, shifting the equilibrium to the right.

Exam Tip

Think of an exothermic reaction like a heater. If you turn the heater down (decrease temperature), the system "panics" and tries to work harder to produce more heat (shifts right). If it were an endothermic reaction, it would be the opposite!