Chapter 13, Problem 71A

Interpretation Introduction

Interpretation: It is to be explained why vapor pressure does not change with the volume of the container.

Concept introduction:

A liquid is a nearly incompressible fluid and has the shape of its container and maintains a (almost) constant volume under all conditions of pressure. The volume is fixed if the temperature and pressure are both constant.

Answer to Problem 71A

Because vapor pressure depends upon the temperature of the liquid only.

Explanation of Solution

Only the kinetic energy of the molecules that are leaving determines vapor pressure. Vapor pressure rises with temperature and is a measurement of a substance's tendency to transform into a gaseous or vapor state. This is because the kinetic energy of a liquid's molecules increases along with the temperature. The number of molecules vaporizing also increases as a function of the molecules' increasing kinetic energy, which increases the vapor pressure.

Thus, the change in the volume of the container does not affect its vapor pressure.