Chapter 12, Problem 78A

Interpretation Introduction

Interpretation:

The relationship among vapor pressure, atmospheric pressure and boiling point must be explained.

Concept introduction:

Vapor pressure is the pressure of the vapor accumulated over a liquid in closed container at saturated condition.

Answer to Problem 78A

At boiling point the vapor pressure of any liquid is equal to atmospheric pressure.

Explanation of Solution

Boiling point of a liquid is the temperature at which the liquid starts boiling and the temperature remain same until all the liquid is converted to vapor.

Boiling point is proportional to the pressure. If pressure is increased then boiling point also increases. For example normal boiling point if water is 100°C. So at 100°C the vapor pressure of water is equal to atmospheric pressure. Now if atmospheric pressure is reduced then water can reach to its boiling point before 100°C as the vapor pressure of water reaches atmospheric pressure.

Conclusion

Vapor pressure of a liquid is equal to atmospheric pressure at boiling point.