Question

In this lab, you will determine the vapour pressure of ethanol (P) at various temperatures and use this data to find the enthalpy of vaporization (ΔvapH).

If a plot of ln P vs. 1/T gives a slope of -9898 K, what is the ΔvapH in kJ/mol? Do not worry about how realistic the value is. Assume R = 8.314 J mol-1 K-1.

Answer 1

The relation between P and T is:

P = A*e^(-Hvap/RT)

taking ln on both sides, above expression becomes,

ln P = ln A - Hvap/RT

So, slope between ln P and 1/T will have a value of -Hvap/R and y intercept is ln A

So,

Here slope = -9898

So,

-Hvap/R = -9898

-Hvap/8.314 = -9898

Hvap = 8.23*10^4 J/mol

Hvap = 82.3 KJ/mol

Answer: 82.3 KJ/mol