Question

if a chemical reaction is reversed, what happens to the enthalpy of the reaction? the enthalpy of the reaction becomes zero. the enthalpy of the reaction doubles. the sign of the enthalpy of the reaction reverses. the enthalpy of the reaction is halved.

Explanation:

Step1: Recall enthalpy property

Enthalpy is a state - function. When a chemical reaction is reversed, the products become reactants and vice - versa.

Step2: Determine sign change

The enthalpy change of a forward reaction has a certain sign. When the reaction is reversed, the sign of the enthalpy change of the reaction also reverses. For example, if a forward reaction is exothermic ($\Delta H<0$), the reverse reaction is endothermic ($\Delta H > 0$) and vice - versa.

Answer:

The sign of the enthalpy of the reaction reverses.