17.1 The Equilibrium Law

The reaction below shows the decomposition of dinitrogen tetroxide, N₂O₄, into two molecules of nitrogen dioxide, NO₂. 

N₂O₄ (g) → 2NO₂ (g)        ΔH = +58 kJ mol^-1

A dynamic equilibrium is reached at a temperature of 298K. The concentrations of each of the compounds at equilibrium are shown in the table below.

	N2O4	NO2
Concentration at equilibrium (mol dm-3)	0.0647	0.0206

Give the expression for K_c for this reaction.

[1]

The following reaction was allowed to reach equilibrium at 761 K.

H₂ (g) + I₂ (g)  2HI (g)               ΔH^θ < 0

State the equilibrium constant expression, K_c , for this reaction.

[1]

Comment on whether this reaction is feasible.

[1]

Methanoic acid and methanol react to form the ester methyl methanoate and water as follows:

H₂COOH (I) + CH₃OH (I) ⇌ HCOOCH₃ (I) + H₂O (I)

At 35 ^oC, the free energy change, ΔG, for the reaction is -3.79 kJ mol^-1.

Using sections 1 and 2 of the data booklet, calculate the value of K_c for this reaction to 2 decimal places.

[2]

Using your answer to part (a), predict and explain the position of the equilibrium.

[2]

The value for ΔG = -4.21 kJ mol^-1 as the temperature is increased to 50°C.

State what happens to the value of the equilibrium constant.

[1]