Question

Which of the following is likely to be true about the ΔH for this reaction?

Answer 1

I would say A.

Because it is cooling down, going from liquid to solid, so it is loosing energy. THis energy must be being released to the surroundings so 

Answer 2

Answer: Option (a) is the correct answer.

Explanation:

Enthalpy is defined as the total amount of heat present in a system.

When there is bond formation in a chemical reaction then it means energy is released. Hence, the reaction is exothermic in nature and $\Delta H$ < 0 or negative.

On the other hand, when breaking of bonds occurs then energy is absorbed by the system. Hence, the reaction is endothermic in nature and $\Delta H$ > 0 or positive.

Thus, in the given reaction $C_{6}H_{6}(l) \rightarrow C_{6}H_{6}(s)$, the state is changing from liquid to solid.

This means atoms are coming close to each other and hence, there is occurrence of bond formation. As a result, energy will be released to the surroundings.

Hence, we can conclude that H < 0 for the given reaction.