Consider a binary mixture of methyl ethyl ketone (component 1) and toluene (component 2). At 323 K the activity coefficients γ₁ and γ₂ are given by
ln γ₁=x₂²(ψ₁-ψ₂+4ψ₂x₁)
ln γ₂=x₁²(ψ₁+ψ₂-4ψ₂x₂)
where x₁ and x₂ are the mole fractions in the liquid mixture, and ψ₁ and ψ₂ are parameters independent of composition. At the same temperature, the infinite dilution activity coefficients, γ₁^∞ and γ₂^∞ are given by lnγ₁^∞=0.4 and lnγ₂^∞=0.2. The vapour pressures of methyl ethyl ketone and toluene at 323 K are 36.9 and 12.3 kPa respectively. Assuming that the vapour phase is ideal, the equilibrium pressure (in kPa) of a liquid mixture containing 90 mol % toluene is