Question

ü.
Consider the following system at constant pressure. Indicate whether the work is done by the system
or on the system. Also indicate if there is no work done.
H2(g) + Cl2(g) → 2HCl(s)​

Answer 1

Formation of HCl is an exothermic reaction.

Explanation:

Work done = -P(∆V)

Since pressure is a constant, work done only depends on the volume. Exothermic reactions are the reactions in which heat is liberated and Endothermic reactions are those in which heat is absorbed. Here we can see that ∆V is negative, that is, it is an exothermic reaction which liberates heat.

Answer 2

There is no work done during the formation of HCl.

• Consider the work equation, W = -ΔnRT, when Δn = 0 ⇒ W = 0
• In the case of formation of HCl, work done, W = 2-2 = 0, this implies that there is no work done.
• Hydrochloric acid is prepared from hydrogen gas and chlorine gas in the presence of sunlight, this is an exothermic reaction resulting in the work done to be zero.