Areaction a(aq) + b(aq) > c(aq) has a standard free‑energy change of − 3.87 kj / mol at 25 °c.
1. 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?

The concentration of A, B and C is 0.14 M, 0.24 M and 0.16 M respectively.

Explanation:

Relation between standard Gibbs free energy and equilibrium constant follows:

where,

= standard Gibbs free energy = -3.87 kJ/mol = -3870 J/mol  (Conversion factor: 1 kJ = 1000 J)

R = Gas constant =

T = temperature =

= equilibrium constant in terms of concentration

Putting values in above equation, we get:

The given chemical reaction follows:

Initial:           0.30     0.40          0

At eqllm:     0.30-x   0.40-x        x

The expression of for above equation follows:

We are given:

Putting values in above expression, we get:

Neglecting the value of x = 0.75 because the equilibrium concentration cannot be greater than initial concentration.

So, concentration of A = (0.30 - x) = (0.30 - 0.16) = 0.14 M

Concentration of B = (0.40 - x) = (0.40 - 0.16) = 0.24 M

Concentration of C = x = 0.16 M

Hence, the concentration of A, B and C is 0.14 M, 0.24 M and 0.16 M respectively.

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