Chapter 9, Problem 21Q

(a)

Interpretation Introduction

Interpretation:

The effect of intermolecular forces on rate of evaporation has to be explained.

Concept introduction:

• Evaporation is a phenomenon applicable to liquids. It is defined as the transition from liquid   phase to vapor phase in liquids. This transition occurs either by spontaneously without any    external energy or in the presence of external energy. The rate of evaporation is affected by various factors.

• Intermolecular force is defined as the interactions between the components of a substance. The strength of interaction depends upon the type of components.

• If the components are ions of unlike charges, as in the case of ionic compounds, the interaction is quite strong which is called electrostatic force of attraction.

• When the components are non-polar neutral molecules, as in the case of covalent compounds, the intermolecular forces present are Van der Waals forces and London dispersion forces.

• When the components are of polar nature as in the case of polar covalent compounds, there can be hydrogen bonding, dipole-dipole forces acting between them.

• Each of these forces is not of equal strength. Thus different compounds have different kind of intermolecular forces and hence different properties.

(b)

Interpretation Introduction

Interpretation:

The effect of temperature on rate of evaporation has to be explained.

Concept introduction:

      Temperature is measure of average kinetic energy possessed by the molecules. Thus, temperature of a substance implies the average kinetic energy possessed by its molecules. Temperature is measured in different scales like Celsius, Kelvin or Fahrenheit.  If the freezing point of water is said to be ${\text{0}}^{\text{o}}\text{C}$, the term ${\text{0}}^{\text{o}}\text{C}$ indicates the average kinetic energy of water molecules. It implies, the water molecules are not in movement and have almost zero energy in frozen state.

(c)

Interpretation Introduction

Interpretation:

The effect surface area on rate of evaporation has to be explained.

Concept introduction:

     Surface area is the region corresponding to the surface of the molecules. It is associated with the size of the molecules. If the size is large, surface area is high. Molecules with high surface area get more exposure to surroundings.