Boyle’s Law
Jhoann D. Reyes, R.N., LPT, MAEd
GAS
• Gas is the state of matter that has particle that are freely
moving and are widely far from each other which makes them
highly compressible, and gases have undefined shape and
volume.
• Common gases: Air, Natural Gas, Oxygen, Carbon Dioxide,
Nitrogen, Water Vapor, Helium, Argon.
PROPERTIES OF GASES
• Gases can completely fill up the container in which they are placed due to its undefined shape and volume.
• Two or more gases can be readily mixed evenly and completely when combined because gases diffuse very
rapidly.
• The wide spaces between gas particles make gases compressible and expandable depending on the
pressure applied to it. Gases expand when pressure is reduced. Gases compress when pressure is
increased.
• Gases are less dense compared to other states of matter. Their density varies as the temperature and
pressure changes. The density of the air is 0.0012g/cm3 .
• Gases have mass.
• Gases exert constant uniform pressure in all directions on the wall of their containers.
• Gases have important fundamental properties that are measurable such as volume, pressure, temperature,
and amount of the gas or number of moles.
BOYLE’S LAW
• The law was named after chemist and physicist Robert Boyle, who
published the original law in 1662.
• Robert Boyle was able to investigate the relationship between pressure
and volume of a gas using a J-shaped tube apparatus, which is closed
on one end.
• Boyle’s law states that the volume of a given mass of gas held at
constant temperature is inversely proportional to its pressure.
• Its formula is: P1V1 = P2V2 , where P1 and V1 are the initial volume; while,
P2 and V2 are the final pressure and volume of the same amount of gas
at the same temperature.
SAMPLE PROBLEM #1
• At 35°C a sample of nitrogen gas occupies 600mL under a
pressure of 760 torr. Determine the volume of this gas at a
pressure of 3.00 atmospheres at the same temperature.
SOLUTION
• Given: P1 = 1 atm, since 760 torr = 1 atm
V1 = 600 mL
P2 = 3 atm
V2 = ?
Solution:
P1V1 = P2V2
= (1 atm) (600 mL) = (3 atm) (x)
= (600 mL · atm) / (3 atm) = x
V2 = 200 mL
SAMPLE PROBLEM # 2
• A pressure of 850 kPa is required to initially inflate the
balloon .27 L . What is the final pressure when the
balloon has reached its capacity of 1.2 L .
SOLUTION
• Given: P1 = 850 kPa
V1 = .27 L
P2 = ?
V2 = 1.2 L
Solution:
P1V1 = P2V2
= (850 kPa) (.27 L) = (x) (1.2 L)
= (229.5 kPa · L) / (1.2 L) = x
P2 = 191.25 kPa
APPLICATION OF BOYLE’S LAW
• Breathing or respiration is one of the basic applications of Boyle’s law. As one inhales, the diaphragm
muscles contract causing the thoracic cavity to expand. The expansion increases the volume and
results in the decrease of pressure. Meanwhile, as one exhales, the muscles relax causing the
thoracic cavity to decrease in volume. This causes an increase in pressure inside the lungs; thus,
pushing the air out.
• Deep sea fishes when brought to the surface, die due to a decreased pressure. This results in the
increased volume of gases in their bodies.
• A syringe plunger being pressed down to draw out the fluid causes the volume inside the syringe to
decrease while increasing the pressure inside.
• In an aerosol can, the contents are mixed with a gas under pressure high enough to render the gas
into a liquid. When the nozzle is opened, however, this reduces the pressure suddenly, allowing the
gas to expand. As it does so, it forces its way out of the nozzle, carrying the contents with it. The
same effect occurs when a pressurized soda can is opened, allowing pressurized carbon dioxide to
form bubbles in the beverage.