The following reaction is used industrially to produce a combustible gas from coal: H 2 O(g) + C(s) H 2 (g) + CO(g) A mixture of powdered coal and steam at a pressure of 1 atm and a temperature of 1300 o C was allowed to reach equilibrium. It was found that he 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 K p including its units. (ii)Use the data given to calculate the partial pressures of hydrogen and carbon monoxide and hence calculate a value for K p

K p = P H2 x P CO P H20 H 2 O(g) + C(s) H 2 (g) + CO(g) 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 H 2 and 1 mol of CO, partial pressure of H 2 = partial pressure of CO = partial pressure of steam used = 0.9 atm. K p = P H2 x P CO = 0.9 x 0.9 = 8.1 P H20 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 H 2 and CO is 1.9 – 0.1 = 1.8. Since the same amounts of H 2 and CO are produced in the reaction, partial pressure of H 2 = partial pressure of CO = 0.5 x 1.8 = 0.9 atm.