1. Kp

2. The equilibrium constant in terms of partial pressuresKp
The equilibrium constant in terms of partial pressures

3. Mole fraction

4. 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) = = 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

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

6. 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 =
= kPa–1 x

7. 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)