Question

Given the following information, calculate the standard Gibbs free energy of the reaction at 1455 K. State if the reaction is spontaneous or nonspontaneous followed by the temperature at which the reaction switches spontaneity if applicable.

CaCO₃(s) --> CaO(s) + CO₂(g)

Given: Δ°H = 179.2 kJ , Δ°S = 160.2 J/K

Answer 1

1)

deltaHo = 179.2 KJ/mol

deltaSo = 160.2 J/mol.K

= 0.1602 KJ/mol.K

T = 1455 K

we have below equation to be used:

deltaGo = deltaHo - T*deltaSo

deltaGo = 179.2 - 1455.0 * 0.1602

deltaGo = -53.891 KJ/mol

since delta Go is negative, the reaction is spontaneous

Answer: -53.891 KJ/mol, spontaneous

2)

deltaHo = 179.2 KJ/mol

deltaSo = 160.2 J/mol.K

= 0.1602 KJ/mol.K

we have below equation to be used:

deltaGo = deltaHo - T*deltaSo

for reaction to be spontaneous, deltaGo should be negative

that is deltaGo<0

since deltaGo = deltaHo - T*deltaSo

so, deltaHo - T*deltaSo < 0

179.2- T * 0.1602 < 0

T * 0.1602 > 179.2

T > 1119 K

Answer: 1119 K