Question

Write applications of standard molar entropy°.

Answer 1

Applications of standard molar entropy:

1) ΔSº for a chemical reaction can be calculated by knowing the values of standard
molar entropy of all reactants and products in the reaction. It is obtained by
subtracting total standard molar entropy of all the reactants from those of all the
products. The entropy change for the reaction is thus given by,

ΔS° = `summ S^@` (products) `sumn S^@` (reactants)

where, m and n are the coefficients of products and reactants respectively in the
balanced equation.

eg. aA + bB → cC + dD

ΔS° is given by,

ΔS° = `(cS_c^@ + dS_D^@) - (aS_A^@ + bS_B^@)`

The standard molar entropy is useful in comparing the entropies of different
substances under the same conditions of temperature and pressure.

The S° values increase with increasing complexity of molecules.

eg. CH₃COOH is more complex than CH3OH. Hence S° of CH₃COOH
(160 J K^-1 mol1) is larger than that of CH3OH (127 J K1 mol^-1)

The S° values of the heavier substance are larger than those of the lighter substance.

eg. For I_(g), S° = 180.7 J K^-1 mol1 whereas for F(g), S° = 158.6 J K^-1 mol^-1.