Question

The saturation pressure for an unknown substance has been fitted to temperature using the

following Antoine’s equation:

lnPsat = 8.6866 − (2626.42/(T −146.6))

where [Psat] = [bar] and [T] = [K]. Estimate the heat of vaporization of this substance at the

normal boiling point.

Answer 1

Given Antoine’s equation is

At normal boiling point, vapor pressure becomes equal to the atmospheric pressure at sea level, i.e., 1 atm.

Therefore, P^sat = 1 atm = 1.01325 bar

Now, using Antoine’s equation,

Now, to calculate the heat of vaporization we need to use Clausius Clapeyron equation, which is

, where C is a constant.

We assume two temperature values of 400K and 500K (up and down to T = 449.4 K) and then substitute them in the Antoine’s equation to get the values as shown in the Table here.

This is the estimated heat of vaporization for the unknown substance at normal boiling point (T=449.4 K)