Boyle's Law

Boyle's law is one of the gas laws that illustrates the relationship between pressure and volume of gases at constant temperature. This law was analyzed by Robert Boyle in 1662. In his experiment, he varied the pressure and observed its effect on the volume of the gas without changing its temperature.

This law states that if a pressure of a gas is increased, the volume of the gas is decreased. Study the following figures.

This law can be mathematically expressed as:

P1V1=P2V2

where:

• P1 = initial pressure
• V1 = initial volume
• P2 = final pressure
• V2 = final volume

Any units of pressure and volume may be used. However, uniformity must be observed.

Pressure Units

• 1 atmosphere (atm) = 760mm Hg = 760 torr = 150000 Pascal (Pa)

Volume Units

• 1 Liter = 1000 mL
• 1mL = 1 cm3

Problem Solving Reminders:

• Analyze the given problem.
• List down the given values and what is asked.
• Identify the formula to be used.
• Write solutions clearly.
• Analyze if you have the correct answer.

Sample Problem #1:

Two hundred milliliter of gas is contained in a vessel under a pressure of 850mm Hg. What would be the new volume of the gas if the pressure is changed to 1000mm Hg?

• 
  Given:
  P1= 850 mm Hg
  V1= 200 cm3
  P2= 1000 mm Hg
  V2= ?
  Equation: P1V1 = P2V2
• Solution:
  P1V1 = P2V2
  (850mm Hg)(200cm3)=(1000mm Hg) V2
  (850mm Hg)(200cm3)= V2
  (1000mm Hg)
  170 cm3 = V2

Sample Problem #2:

A 2.5 liter sample of a gas is collected at a pressure of 1.25 atm. Calculate the pressure needed to reduce the volume of a gas to 2.0 liters. The temperature remains unchanged.

• Given:
  P1= 1.25 atm
  V1= 2.5 liter
  P2= ?
  V2= 2.0 liters
  Equation: P1V1 = P2V2
• 
  Solution:
  P1V1 = P2V2
  (1.25 atm)(2.50 L) = P2 (2.0 L)
  (1.25 atm)(2.50 L) = P2
  (2.0L)
  P2 = 1.56 atm