In the reaction: M + N → P ΔH = +Q kJ Which of the following would increase the concentration of the product?

Analysis

The reaction is given as: M + N ⇌ P with ΔH = +Q kJ.

• The positive sign of ΔH (+Q) indicates that the reaction is endothermic (it absorbs heat).
• According to Le Chatelier’s Principle, if a system at equilibrium is subjected to a change in concentration, temperature, or pressure, the system will adjust itself to counteract that change.

Concept: Le Chatelier’s Principle

1. Temperature: For an endothermic reaction, heat acts like a reactant. Increasing the temperature shifts the equilibrium to the right (forward) to absorb the excess heat, thereby increasing the concentration of the product (P).
2. Concentration: Increasing the concentration of reactants (M or N) shifts the equilibrium to the right. Increasing the concentration of the product (P) would shift the equilibrium to the left (reverse).
3. Catalyst: A catalyst increases the rate of both forward and backward reactions equally. It helps the system reach equilibrium faster but does not change the position of the equilibrium or the concentration of the products.

Step-by-Step Solution

• Option A: A catalyst only speeds up the reaction; it does not increase the yield of the product.
• Option B: Increasing the concentration of P would cause the system to shift to the left to consume the excess P, decreasing the yield.
• Option C: Since the reaction is endothermic (ΔH > 0), adding heat (increasing temperature) forces the reaction to move forward to use up the heat, thus producing more P.
• Option D: Decreasing the temperature would shift the equilibrium to the left (the exothermic direction), decreasing the concentration of P.

Conclusion

Increasing the temperature is the correct way to shift an endothermic reaction toward the product side.

Exam Tip: Remember the mnemonic "Endo-Heat-In": For Endothermic reactions, adding Heat shifts the reaction In (forward) to the product side. Conversely, for Exothermic reactions, cooling the system increases the product yield.