Chapter 14, Problem 25A

Interpretation Introduction

Interpretation:

Vapor pressure of liquid is to be determined and how does vapor pressure develop in a closed flask containing liquid is to be described.

Concept introduction:

The vapor pressure of a liquid is the equilibrium pressure of a vapor above its liquid surface in a closed container. The evaporation process changes the phase of liquid molecules to gas while the condensation process changes the phase of gas molecules into liquid.

Answer to Problem 25A

The vapor pressure is a pressure of vapor above its liquid surface in a closed container. The evaporation and condensation processes are going on in the flask. It is when the two are at equilibrium and applies only to a closed container.

Explanation of Solution

When the small amount of liquid is first placed into a closed container, some particles of liquids will change its phase from liquid to gas and move into the gas above the liquid surface, this process is known as evaporation. Similarly, due to the increased vapor pressure the particles in the gas phase will also move back into the liquid phase, this process is known as condensation.

The rate of these particles moving into the gas phase (evaporation) is same as the rate of particles moving back into the liquid phase (condensation) that are at equilibrium.

Conclusion

At equilibrium, rate of evaporation is same as rate of condensation in a closed container.