Question

The reaction ?2?12 (g) ⇆ ?4?6(g) + ?2?6(g) is at equilibrium at 1 bar at 700 K.
You may assume that there are no competing reactions when cyclohexane (C6H12) is heated to 700

K, and you may treat all gases as ideal (perfect) gases.

(a) Write an expression for the equilibrium constant, K, in terms of partial pressures. State the units of pressure in your expression.

(b) The partial pressure of each gas was measured for the above reaction at equilibrium:? C₆H₁₂ = 0.1824 bar, ?C₄H₆= ?C₂ H₆= 0.4088 bar. Calculate the value of K at 700 K.

(c) What happens to the value of K when the total pressure is raised to 2 bar at 700 K?

(d) What happens to the position of equilibrium when the total pressure is raised to 2 bar at 700 K? Explain your answer using an equation involving the mole fractions of reactants and products.

Answer 1

a)

The expression of equilibrium constant in terms of partial pressure is as

K = (P_C4H6) (P_C2H6)/(P_C6H12) bar

b)

K = (0.4088) (0.4088)/(0.1824) bar
K = 0.9162 bar

The value of K at 700 K = 0.9162

c)

On increasing the total pressure of the reaction does not alter the equilibrium constant.

d)

According to Le-Chatelier principle, when total pressure of the reaction is raised to 2 bar at 700 K, the position of equilibrium will shift towards reverse. This is because the volume of the product is more than the reactant.i.e. the mole fraction of product is higher than the reactant.