# The heat content of the products is more than that of the reactant in an ............. reaction

The heat content of the products is more than that of the reactant in an ............. reaction.

In this question the answer given is "exothermic"; yet I thought the answer would be endothermic as the products have more heat content and energy cannot be created nor destroyed. Therefore, from the reactants' side, more energy should have been put in for the heat content of the products to be greater.

Also mathematically endothermic make sense as: $$\Delta_\mathrm{r}H = \sum \Delta_\mathrm{f}H_\mathrm{P}-\sum \Delta_\mathrm{f}H_\mathrm{R}$$

And as: $$\sum \Delta_\mathrm{f}H_\mathrm{P} \gt \sum \Delta_\mathrm{f}H_\mathrm{R}$$ ,$$\Delta_\mathrm{r}H \gt 0$$

Could someone please explain where am I wrong and why the answer is 'exothermic'?

• The IUPAC Gold Book definition for exothermic is that the std. enthalpy change ($\Delta H^o$) ("$^o$" =1 bar) is negative (goldbook.iupac.org/terms/view/E02269). That means if you did the reaction at 1 bar in a diathermal container, q would be negative (heat flow out of the system). Now suppose you did the same reaction at const. P (1 bar), but adiabatically. The latter describes a constant-pressure calorimeter (look it up). The walls are insulated, but P is kept constant. In that case, the energy released by the rxn causes an increase in T (even if some of that energy also goes towards work). Aug 7, 2019 at 20:43