The ∆Hvap for acetone is 29.1 kJ/mol at its boiling point of 56.2 °C. Calculate ∆E for the vaporization of one mole of acetone at this temperature.

Answer 1

Hi Stella C.!

To answer this question, we must first start with the definition of enthalpy:

H = E + PV

While we have the value for enthalpy, H, we do not know the values for the pressure and volume. Consequently, we must substitute in values for terms which we actually do have. In this way, we can find the ideal gas law a convenient substitute. Let's have a go:

H = E + PV

=> PV = nRT (ideal gas law) => PΔV = ΔnRT (because the number of moles of gas are changing, so too will our volume occupied by the acetone species)

ΔH = E + ΔnRT => E = ΔH - ΔnRT

<=> 29.1 kJ*mol^-1 - (1 mol)(8.314 x 10^-3 kJ*mol^-1*K^-1)(273 + 56.2)

ΔE = 26.4 kJ

Hope this helps!

Cheers