Question

A certain reaction has an enthalpy value of -56.4 kJ moll. Assume this value remains constant in the temperature range being studied. The standard Gibbs free energy for the reaction is -241 kJ mol-'at 25.0 °C. What is the standard Gibbs free energy for the reaction at 50.0 °C?

Answer 1

Given data

Enthalpy H = - 56.4 kJ/mol

At temperature T1 = 25°C + 273 = 298 K

Standard Gibbs free energy G1 = - 241 kJ/mol

Temperature T2 = 50°C + 273 = 323 K

Standard Gibbs free energy G2 =?

G1 = H - T1*S1

-241 kJ/mol = - 56.4 kJ/mol - 298K * S1

S1 = 0.61946 kJ/mol·K

S2 = H/T2

= ( - 56.4 kJ/mol) / (323K)

= - 0.17461

Change in entropy

S = S2 - S1

= - 0.17461 - 0.61946

= - 0.79407 kJ/mol·K

G2 = H - T2*S

= - 56.4 kJ/mol - 323K * ( - 0.79407 kJ/mol·K)

= 200.08 kJ/mol