Here is a generic thermochemical equation involving reactants A and B and products C and D: A + 2B 2C + D + 78.3 kJ
What does the expression + 78.3 kJ signify?
An endothermic reaction that releases 78.3 kJ of heat regardless of the amounts of reactants

An exothermic reaction that releases 78.3 kJ of heat regardless of the amounts of reactants

An endothermic reaction that absorbs 78.3 kJ of heat per mole of reactant A

An exothermic reaction that releases 78.3 kJ of heat per mole of reactant A