Question

A balanced chemical reaction that includes the heat change (evolved or absorbed H) during the reaction is called the thermochemical reaction. For exothermic and endothermic reactions, the value of enthalpy change respectively is


a. H > 0, H < 0
b. H > 0, H = 0
c. H = 0, H < 0
d. H < 0, H > 0
e. H = 0, H = 0

Answer 1

Answer: d. H < 0 (exothermic), H > 0 (endothermic).

Explanation: Exothermic reactions release heat so the enthalpy of products is lower than reactants (ΔH < 0). Endothermic reactions absorb heat so enthalpy increases (ΔH > 0).