Question

A reaction A ( aq ) + B ( aq ) − ⇀ ↽ − C ( aq ) has a standard free‑energy change of − 5.46 kJ / mol at 25 °C. What are the concentrations of A , B , and C at equilibrium if, at the beginning of the reaction, their concentrations are 0.30 M, 0.40 M, and 0 M, respectively?

How would your answers change if the reaction had a standard free‑energy change of + 5.46 kJ / mol?

a. There would be no change to the answers.

b.All concentrations would be lower.

c.There would be more A and B but less C .

d. There would be less A and B but more C .

e.All concentrations would be higher.

Answer 1

Standard free energy change of the reaction 4Gº = -5.46 kJ/mol = -5.46x109 J/mol Gas constant, R= 8.314 JK-mo1-1 Temperature, T = 25°C+273 = 298 K Standard free energy change of the reaction, Agº = - RT in K AG In K=- RT -5.46x10 J/mol 8.314 JK-'m01-+x 298 = 2.204 Equilibrium constant, K = 2.204 = 9.06 - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - C(aq) Equilibrium equation: A(aq) + B(aq) = Equilibrium constant, K. = 9.06 ICE tables: A + B A Initial (M): 0.30 0.40 Change (M): -x -X Equilibrium (M): 0.30- X 0.40-X C . , Equilibrium constant, K um constant, AB [C] = (x) 9.06 = (0.30- x)(0.40- x) x = 0.20 According to the ICE table, Equilibrium concentration of A, [A] =(0.30- x)M = (0.30-0.20) M = 0.10 M Equilibrium concentration of B,[B] = (0.40-x)M = (0.40-0.20) M= 0.20 M Equilibrium concentration of C,[C] =(x) M = 0.20 M - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - When the value of Gem is negative( -5.46 kJ/mol), the reaction is spontaneous which means more and more amount of 'C' will be produced. When the value of AG n is positive (+5.46 kJ/mol), the reaction is nonspontaneous which means very less amount of 'C' will be produced. Thus, there would be more 'A' and B'but less 'C' when the std free energy is changed from -5.46 kJ/mol to +5.46 kJ/mol.