The Heat of a reaction is given as the heat content/heat of formation/enthalpies of the products minus the heat content/heat of formation/enthalpies of the reactants. If the potential energy diagram has the product(s) having a higher potential energy than the reactant(s), then the reaction is an endothermic reaction (this is why the reaction absorbs heat from the surroundings to try to make up for the lack of potential energy of the reactants) and the sign on the enthalpy change is visibly positive since H(products) > H(reactants) If the potential energy diagram has the reactant(s) having a higher potential energy than the product(s), then the reaction is an exothermic reaction (this is why the reaction releases heat to the surroundings to try to take care of the higher potential energy of the reactants) and the sign on the enthalpy change is visibly negative since H(reactants) > H(products).
Explanation:
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