Question

The normal boiling point of diethyl ether is 34.50 °C, and the enthalpy of vaporization (∆vapH°) is 26.52 kJ/mol . Assuming that ∆vapH° does not vary with temperature, (i) calculate the vapor pressure of diethyl ether at 50 °C. (ii) Did the vapor pressure increase with temperature? Explain.

Answer 1

use the Clausius-Clapeyron Equation to find out vapour pressure.

ln (P₁ / P₂) = (Δ_vapH / R) (1/T₂ - 1/T₁)

given value Δ_vapH = 25.52 KJ/mol, T1 = 50 ^oC (323.15 ^oK), T2 = 34.50 ^oC (307.65 ^oK), P2 = 760 mmHg (at boiling point), R = gas cons.(8.314 J/K.mol) P1 = ?

ln (P1 / 760 mmHg) = { (25520 J/mol) / (8.314 J/K.mol) } { 1/307.65) - (1/323.15) }

ln (P1 / 760 mmHg) = 0.47856

ln P1 - ln [760 mmHg] = 0.47856

lnP1 = 7.11187

P1 = e^7.11187 = 1226.438 mmHg

yes vapour pressure increases with temperature