Calculate the enthalpy of vaporization of a substance that has a vapor pressure of 55.0 mm Hg at -28.0 °C and?
Calculate the enthalpy of vaporization of a substance that has a vapor pressure of 55.0 mm Hg at -28.0 °C and 632 mm Hg at 27.4 °C. What is the vapor pressure of the substance at 50.9 °C?
More Questions From This User See All
Answers & Comments
Verified answer
We need to use this http://en.wikipedia.org/wiki/Clausius%E2%80%93Clap...
ln (p2/p1) = -ΔH/R (1/T2-1/T1)
1) We need to re-arrange this to make ΔH the subject
ln (p2/p1) = -ΔH/R (1/T2-1/T1)
ln(p2/p1) = ΔH/R ( T2-T1 / T1T2)
(ln(p2/p1)/(T2-T1 / T1T2))R = ΔH
ΔH = (ln(632/55)/(300.4K - 245K / 300.4K*245K) 8.314 J K-1 mol-1 = 27.0 kJ mol-1
2) We need to re-arrange the equation to make p2 the subject of the equation
ln(p2/p1) = ΔH/R ( T2-T1 / T1T2)
(p2/p1) = e^(ΔH/R ( T2-T1 / T1T2))
p2 = p1 x e^(ΔH/R ( T2-T1 / T1T2))
We will use p1 55 mm Hg and T1 as -28°C (245K)
p2 = 55 mm Hg x e^(27000 J K-1 mol-1 / 8.314 J K-1 mol-1 (323.9 K - 245 K / 245K*323.9K))
p2 = 1389 mm Hg