Question

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

A. The enthalpy of the reaction becomes zero.

B. The enthalpy of the reaction doubles.

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

D. The enthalpy of the reaction is halved.

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.