Chapter 14.2, Problem 3RQ

Interpretation Introduction

Interpretation: The use of barometer to measure the vapor pressure needs to be explained.

Concept introduction: Vapor pressure can be defined as the pressure of the vapor present at with its liquid at equilibrium.

Vapor pressure of a liquid can be measured by barometer. A barometer is a tall vertical closed tube standing upside down placed in a dense liquid called mercury.

Answer to Problem 3RQ

The is calculated by using the formula $P=\rho gh$

• $P=$ pressure of the liquid.
• $\rho =$ density of the liquid.
• $g=$ gravity.
• $h=$ height of the column of mercury.

Explanation of Solution

If we inject a few drops of liquid at the bottom of the column, it will rise to the top of mercury by floatation. The liquid at the top starts vaporizing and the vapor formed creates a pressure that thrust some mercury out of the tube and reduces the mercury level. When the equilibrium is achieved mercury level stops changing. The vapor pressure can be determined by using the formula $P=\rho gh$ after calculating the change in the height (h) of the mercury column.

Conclusion

The is calculated by using the formula $P=\rho gh$

• $P=$ pressure of the liquid.
• $\rho =$ density of the liquid.
• $g=$ gravity.
• $h=$ height of the column of mercury.