Question

For which of the processes below will δs be a positive number? 1) ch4(g) → ch4(l) 2) n2h4(g) → n2(g) + 2h2(g) 3) h2o(s) → h2o(g)

Answer 1

The entropy of the gaseous substance is more in comparison to the liquid or solid form of the same substance at same temperature and pressure conditions.

More is the number of particles more will be the entropy of the system.

In the first chemical reaction, CH₄ (g) → CH₄ (l)

Since, the reactants are in gaseous phase and the products are in liquid phase, the entropy is decreasing during the reaction.

In the second chemical reaction,

N₂H₄ (g) → N₂ (g) + 2H₂ (g)

Since, one mole of the reactant in gaseous phase is decomposing to produce three moles of product in gaseous phase, the entropy is increasing during the reaction.

In the third chemical reaction, H₂O  (s) → H₂O (g)

Since, the reactant is in solid phase and product are in gaseous phase. The entropy is increasing during the reaction.

Thus, the entropy is increasing in the 2nd and 3rd reactions.