Question

The change in entropy, ΔS°rxn, is related to the the change in the number of moles of gas molecules, Δngas. Determine the change in the moles of gas for each of the following reactions and decide if the entropy increases, decreases, or has little or no change. H2(g) + Cl2 (g) --> 2HCl(g)

Answer 1

Ans: Change in moles of gas:

Reaction is- H₂(g) + Cl₂(g) 2HCl (g)

No.Of moles of reactants = 1 mole of H₂(g) + 1 mole of Cl₂(g)

= 2 moles of gas molecules.

No. Of moles of products = 2 moles of HCl (g)

Net change in the moles of gas=

moles of gas in product- moles of gas in reactants

=2-2 = 0 moles

As we can see that there is no change in the no. Of moles i.e. same no. Of molecules are involved in reactants and in products . Also all the molecules are diatomic and of similar complexity , so we can't predict the change in entropy i.e. we cannot tell whether the entropy will increase or decrease but we can tell that the change will be very small in magnitude.