The enthalpy of vaporization of water at 100 °C (40.7 kJ mol⁻¹) is much larger than…
CHEMISTRY · Single correct · A Level · Chemistry · Energetics · Energetics
Problem
The enthalpy of vaporization of water at 100 °C (40.7 kJ mol⁻¹) is much larger than its enthalpy of fusion at 0 °C (6.01 kJ mol⁻¹). Which statement best explains this difference in terms of the energy diagrams for the two processes?
(a) Fusion occurs at a lower temperature, so less energy is needed because temperature and enthalpy are directly proportional.
(b) Because the system must do pV work to expand against atmospheric pressure during vaporization, the required energy is greater than for fusion, where the volume change is negligible.
(c) Vaporization requires complete separation of molecules into the gas phase, so breaking nearly all intermolecular attractions results in a larger energy gap.
(d) Hydrogen bonds are stronger and more numerous in liquid water than in ice, so vaporization needs more energy to break them than melting does.