An exothermic reaction proceeds by the release of heat energy and an endothermic reaction proceeds by the absorption of heat energy.
A) Steam condensing to liquid water releases heat. So this process is exothermic.
B) ΔH = -187 kJ: Exothermic reaction. The sign of the change in enthalpy indicates if the reaction s exothermic or endothermic. Positive values indicate an endothermic reaction while negative values represent exothermic reaction.
C) [tex] 2 Cl_{2} + 7 O_{2} + 130 kcal--->2Cl_{2} O_{7} [/tex]: Endothermic reaction as the heat is a reactant showing that heat is absorbed in the process.
D) Ice melting: Endothermic as we have to provide heat for melting the ice.
E) A chemical cold pack: Endothermic reaction as reaction takes energy from the surroundings making the pack feel cold upon touch.
