Kp

The equilibrium constant in terms of partial pressures Kp The equilibrium constant in terms of partial pressures

Mole fraction    

Partial pressures Partial pressure, p The contribution of a gas towards the total pressure Partial pressure = mole fraction x Total pressure A gas mixture with a total pressure of 320 kPa contains 2 mol of N2(g) and 3 mol of O2(g). Mole fractions Partial pressures Sum of partial pressures = Total pressure p(N2) + p(O2) = 128 + 192 = 320 kPa 2 5 3 5 x(N2) = = 0.4 x(O2) = = 0.6 p(N2) = x(N2)P = 0.4 x 320 = 128 kPa p(O2) = x(O2)P = 0.6 x 320 = 192 kPa

What is Kp Similar to Kc but partial pressures used in place of concentration Equilibrium: 2SO2(g) + O2(g) ⇌ 2SO3(g) Units: Kp = Kp =

Calculating Kp Equilibrium: 2SO2(g) + O2(g) ⇌ 2SO3(g) Partial pressures: SO2(g), 74 kPa; O2(g), 23 kPa; SO3(g), 142 kPa Kp = x Kp = = 0.160 kPa–1 x

Heterogeneous equilibria Equilibrium contains different phases Equilibrium: CaCO3(s) ⇌ CaO(s) + CO2(g) Kp expression contains only gaseous species Kp = p(CO2) Solid species are omitted (solids have no gas pressure)