The ammonia in equilibrium with a 1:3 Nirtrogen and hydrogen mixture a...
Calculation of Kp and Kc for the Reaction 1/2N2 + 3/2H2 ⇌ NH3
Equilibrium Constant - Kp
The equilibrium constant Kp can be calculated using the expression:
Kp = (P(NH3))^2 / (P(N2)^(1/2) * P(H2)^3/2)
where P(NH3), P(N2) and P(H2) are the partial pressures of ammonia, nitrogen and hydrogen respectively at equilibrium.
Given that the ammonia amounts to 16% of the equilibrium mixture, the partial pressures of the gases at equilibrium can be determined:
P(NH3) = 0.16 * 20 atm = 3.2 atm
P(N2) = 0.84 * 20 atm = 16.8 atm
P(H2) = 0.84 * 20 atm * (3/2) = 25.2 atm
Substituting these values into the expression for Kp:
Kp = (3.2)^2 / (16.8^(1/2) * 25.2^3/2)
Kp = 1.8 x 10^-4
Equilibrium Constant - Kc
The equilibrium constant Kc can be calculated using the expression:
Kc = ([NH3]^2) / ([N2]^(1/2) * [H2]^3/2)
where [NH3], [N2] and [H2] are the molar concentrations of ammonia, nitrogen and hydrogen respectively at equilibrium.
Since the equilibrium mixture contains only gases, the ideal gas law can be used to relate the partial pressures and molar concentrations of the gases:
P = nRT/V => n/V = P/RT
where P is the partial pressure, n is the number of moles, V is the volume, R is the gas constant and T is the temperature.
Using this relationship, the molar concentrations of the gases can be calculated:
[NH3] = (P(NH3) / RT) = (3.2 atm / 0.0821 L atm/mol K / 700 K) = 0.0052 M
[N2] = (P(N2) / RT) = (16.8 atm / 0.0821 L atm/mol K / 700 K) = 0.0274 M
[H2] = (P(H2) / RT) = (25.2 atm / 0.0821 L atm/mol K / 700 K) = 0.0411 M
Substituting these values into the expression for Kc:
Kc = (0.0052)^2 / (0.0274^(1/2) * 0.0411^3/2)
Kc = 5.1 x 10^-4
Explanation
The equilibrium constant Kp and Kc are measures of the extent of the reaction at equilibrium, and can be used to predict the direction in which the reaction will