Cl2 is a stable diatomic molecule. It can be decomposed to form two Cl atoms as shown below.
Cl2 → 2Cl(9)
Predict the change in enthalpy (AH) of this reaction.
A) AH is (-); endothermic
B) AH is (+); endothermic
C) AH is (-); exothermic
D) AH is (+); exothermic
E) AH = 0; thermoneutral

Option B: ΔH is (+); endothermic

Explanation:

From the reaction Cl2 → 2Cl(g) given, we can see that the number of moles on the left hand side is 1 while on right hand side, it is 2. This means the number of moles are increasing and it means that the randomness of the system has increased. Also, the bonds are being broken down.

Therefore, the reaction is endothermic. In endothermic reactions, ΔH is positive.

Thus, the correct option is option B.

a. energy is absorbed in the reaction.

if in a given reaction the energy of products is greater than the energy of reactants it means that reaction is endothermic and during the reaction, the energy is absorbed by reactants. in an endothermic reaction, the products have more stored chemical energy than the reactants. and in this reaction the reactants are more stable than products before the compounds with less energy are always more stable.