Question

If a chemical reaction is reversed, what happens to the enthalpy of the reaction?

Answer 1

In a chemical reaction is reversed, the one that happens to the enthalpy of the reaction is : C. The sign of the enthalpy of the reaction reverses

It's one of Hess' Law : reversing an equation means reversing the sign of entalphy value

Hope this helps

Answer 2

Answer:   C. The sign of the enthalpy of the reaction reverses.

Explanation: Enthalpy of a reaction is the net heat absorbed or released  during a chemical reaction.It is represented by $\Delta H$. It is negative for exothermic reactions in which heat is released and is positive for endothermic reactions in which heat is absorbed.

When a chemical reaction is reversed the heat of the reaction changes its sign.

$CaCO_3\rightarrow CaO+CO_2$   $\Delta H=+ve$

The decomposition of calcium carbonate is an endothermic reaction as heat is required to break the bonds and thus energy is absorbed.

$CaO+CO_2\rightarrow CaCO_3$    $\Delta H=-ve$

When the reaction is reversed, the reaction becomes exothermic as now bonds are getting formed and energy is released.