Predict the sign of entropy change in each of the following :
(I) H2 (at 298 K, 1 atm) →H2 (at 298K, 10 atm)
(II) H2O (at 298 K, 1 atm) →H2O (at 330 K, 1 atm)
(III) 2NH4 NO3(s) → N2(g) +4H2O(g) + 02(g)
(IV) Crystallization of copper sulphate from its saturated solution.
(V) 2SO2(g) + O2 (g) ↔2SO3(g)
Entropy is a measure of randomness or disorder of a system. If randomness increases entropy increases.
(I) Gas at lower pressure has greater randomness thanΔ at high pressure (compressed gas) at the same temperature. Hence, entropy decreases, i.e. ΔS is –ve.
(II) Molecules at higher temperature have greater randomness at the same pressure. Hence, ΔS is +ve.
(III) Gaseous molecules have greater randomness that the solid. Hence, ΔS is positive.
(IV) CuSO4 crystals have ordered arrangement whereas ions in sol. Have greater randomness. Hence ΔS is –ve.
(V) There are 3 moles of two different gaseous reactants which have greater randomness than 2 moles of the only gaseous product, SO3. Hence, randomness decreases i.e. ΔS is –ve.