Consider an ideal gas system. For an exothermic reaction occurring at constant pressure, how does the enthalpy change?

Correct option is A

The correct answer is (a) Negative.
• For a reaction occurring at constant pressure, the enthalpy change (ΔH) equals the heat exchanged (qₚ).
• In an exothermic reaction, heat is released to the surroundings, so qₚ < 0 and therefore ΔH is negative.
Information Booster:
• Enthalpy is a state function, independent of the path taken.
• For an ideal gas, enthalpy depends only on temperature.
• ΔH < 0 → Exothermic reaction
• ΔH > 0 → Endothermic reaction
Additional Knowledge:
• At constant pressure: ΔH = qₚ
• At constant volume: ΔU = qᵥ
• The concept of enthalpy was introduced by Heike Kamerlingh Onnes in 1909.