calculate delta H

Question

Oxygen (O₂) is necessary for cellular respiration; it must be transported from the lungs to tissues through the bloodstream. However, O₂ is not very soluble in water. The Keq of oxygen dissolving at 300.0 K is 7.64 x 10⁻⁴ and the Keq at 320.0 K is 5.23 x 10⁻⁴. Calculate the ∆H(dissolve) for oxygen solubility in water, in kJ/mol.

Answer 1

Use the van’t Hoff equation:

ln(K2/K1) = -ΔH/R (1/T2 - 1/T1)

K1 = 7.64x10^-4

T1 = 300K

K2 = 5.23x10^-4

T2 = 320K

R = 8.314 J/Kmole

ΔH = ?

Solving for ΔH:

ln(5.23x10^-4/7.64x10^-4) = -ΔH/R(1/320 - 1/300)

-0.3790 = ΔH/8.314 (-0.000208)

-0.3790 = - 0.000208ΔH /8.314

ΔH = 15,149 J/ mole = 15.1 kJ/mol