Chapter 6, Problem 1TC

To determine

The definition of latent heat of vaporization and fusion. Also define the one that requires more heat to transform physical state of water and give reason.

Answer to Problem 1TC

Latent heat of vaporization is the amount of heat energy necessary to break the strong hydrogen bonds, and latent heat of fusion is the amount of heat energy that must be removed to form ice. Latent heat of vaporization requires more heat to transform physical state of water since it involves breaking of hydrogen bonds, while the other involves bending.

Explanation of Solution

The diffusion of individual molecules of water occurs into the air during the vaporization or evaporation of water. Each molecule of water is connected to each other with the bonds of hydrogen. Hence, to break those bonds and to allow the molecules to fly away from the surface, heat energy is needed. The amount of heat energy that is required to break the strong bonds of hydrogen is termed as the latent heat of vaporization.

Latent heat of fusion can be defined as the volume of heat energy that must be removed to form the ice. The removal of one calorie of heat from freezing water at 0°C or 32°F does not change its temperature. Instead about 80 calories of heat energy must be removed per gram of pure water at 0°C or 32°F to form ice. This heat is denoted as the latent heat of fusion.

The breaking up of hydrogen bonds occurs in latent heat of vaporization, while bending happens in ice formation. Hence, more energy is required to break than to bend. It indicates that the latent heat of vaporization is greater than the latent heat of fusion.