Chapter U5.3, Problem 3E

Interpretation Introduction

Interpretation:

Energy transferred to a liquid or from a liquid when it evaporates, or when it solidifies needs to be explained.

Concept Introduction :

When two substances are in physical contact with each other but no exchange of heat energy takes place, it is known as thermal equilibrium.

Answer to Problem 3E

A liquid takes energy when it evaporates and when it solidifies, it releases energy.

Explanation of Solution

Energy is needed to alter the phase of object.To break the bond of ice, molecule energy is required so that it melts. During the change of phase, energy might be subtracted or added from the system, but temperature will not change. The change in temperature only occurs when phase change happens.

Latent heat is the heat energy needed to alter the object from one phase to another. Energy is required to alter from solid phase to liquid phase, liquid state to gaseous state,i.e., evaporation or solid state to gaseous state, i.e., sublimation.

• The energy which is used to change liquid into vapor is latent heat of evaporation.
• The energy which is used to change liquid into solid and vice versa is latent heat of sublimation.

So as per the above explanation,energy is transferred to a liquid when it evaporates and it is transferred from a liquid when it solidifies.