Question

The molar enthalpy of vaporization of acetone is less than that of water. Why?

Answer 1

A thermodynamic system's enthalpy is defined as the sum of the system's internal energy and the product of its pressure and volume. It's a state function that's utilised in a variety of measurements in chemical, biological, and physical systems under constant pressure, which the vast ambient environment easily provides.

Complete answer:
The amount of energy (enthalpy) that must be added to a liquid material to change a quantity of that substance into a gas is known as the enthalpy of evaporation, also known as the (latent) heat of evaporation or heat of evaporation. The enthalpy of evaporation depends on the pressure at which the transition occurs.
The enthalpy of evaporation is frequently used to describe a substance's usual boiling temperature. Although tabular values are generally adjusted to 298 K, the error in the observed value is often lower than the error in the adjustment.
The amount of heat required to convert the condition of 1 mole of liquid to gas is known as the molar enthalpy of vaporization. Because acetone molecules lack hydrogen bonds like water molecules, intermolecular attractive forces in acetone molecules are lower than in water molecules, causing it to boil (and evaporate) faster. Water, on the other hand, has strong hydrogen bonds and a high polarity, which causes it to boil at greater temperatures. As a result, the molar enthalpy of water is greater than that of acetone. Water has a higher enthalpy of vaporisation than acetone due to the strong intermolecular force of attraction (hydrogen bonding).

Note:
The heat of evaporation is temperature dependent, however for small temperature ranges and decreased temperatures, a constant heat of evaporation can be assumed. With rising temperature, the heat of evaporation decreases until it entirely disappears at a temperature termed the crucial temperature. The liquid and vapour phases are indistinguishable beyond the critical temperature, and the material is referred to as a supercritical fluid.