The following reaction is used industrially to produce a combustible gas from coal:

H2O(g) + C(s) H2(g) + CO(g)

A mixture of powdered coal and steam at a pressure of 1 atm and atemperature of 1300 oC was allowed to reach equilibrium. It was found thathe total pressure had increased to 1.9 atm but the remaining steam had a partial pressure of only 0.1 atm.

(i) Write down the expression Kp including its units.

(ii) Use the data given to calculate the partial pressures of hydrogen and carbon monoxide and hence calculate a value for Kp

Kp = PH2 x PCO

PH20

H2O(g) + C(s) H2(g) + CO(g)1 0 00.1 0.9 0.9

Initial partial pressure/atm:Equilibrium:

Change in partial pressure of steam = 1 – 0.1 = 0.9 atm.

The steam has reacted to form hydrogen and carbon monoxide

Since 1 mol of steam produces 1 mol of H2 and 1 mol of CO, partial pressure ofH2 = partial pressure of CO = partial pressure of steam used = 0.9 atm.

Kp = PH2 x PCO = 0.9 x 0.9 = 8.1

PH20 0.1

Alternative method: Since the total pressure at equilibrium is 1.9 and the remaining partial pressure of steam is 0.1, the partial pressures of H2 andCO is 1.9 – 0.1 = 1.8.

Since the same amounts of H2 and CO are produced in the reaction, partialpressure of H2 = partial pressure of CO = 0.5 x 1.8 = 0.9 atm.