# Exercise 9 | Chemical Thermodynamics

Calculate ΔH0vap [Br2] given that the vapor pressure of bromine is 133 Torr at 293K and 48.1 Torr at 273K.

Clapeyron-Clausius equation :

ln $\left(\frac{{\mathrm{P}}_{2}}{{\mathrm{P}}_{1}}\right)$ = $\frac{∆{{\mathrm{H}}^{0}}_{\mathrm{rxn}}}{\mathrm{R}}$ x

ΔH0rxn = R ln $\left(\frac{{\mathrm{P}}_{2}}{{\mathrm{P}}_{1}}\right)$ x

Situation 1: P1 = 133 Torr and T1 = 293K

Situation 2: P2 = 48.1 Torr and T2 = 273K

ΔH0vap = 8.314 x ln $\left(\frac{48.1}{133}\right)$ x

ΔH0vap = 33.8 kJ.mol-1