Question

Calculate ΔS_Total  and hence show whether the following reaction is spontaneous at 25°C. 

Hg_(s) + O_2(g) → Hg_(I) + SO_2(g) ΔH⁰ = – 238.6 kJ 

ΔS⁰ = +36.7 JK^-1

Answer 1

Given :

Hg_(s) + O_2(g) → Hg_(I) + SO_2(g)

Δ_rH⁰ = – 238.6 kJ

ΔS⁰ = +36.7 JK^-1

T = 273 + 25 = 298 K

ΔS_Total = ?

ΔS_Total = ΔS_sys + ΔS_surr

Now,

ΔS_sys = 36.7 JK^-1

Since the reaction is exothermic, system loses heat to surroundings. 

Hence the entropy of the surroundings increases. 

ΔH_surr = + 238.6 kJ = 238600 J

∵ ΔS_Total > 0, the reaction is spontaneous.

∴ ΔS_Total = 837.4 JK^-1

The reaction is spontaneous.