Properties of Gases

• Gases have unique properties. Some important properties of gases are listed below.
• Gases have no definite shape or volume, and they expand to completely fill their container.
• Gas particles move rapidly in all directions.
• Gases spread out easily and mix with one another. Unlike solids and liquids, gases are mostly empty space.
• Gases have a very low density because their particles are so far apart. Because of this property, gases are used to inflate tires and balloons.
• Gases are compressible.
• Gases are fluids.

Gas molecules are in constant motion, and they frequently collide with one another and with the walls of their container.

• Gases exert pressure on their containers.
• The kinetic theory helps to explain pressure. Helium atoms in a balloon are constantly hitting each other and the walls of the balloon, as shown below.
• Therefore, if the balloon is punctured, the gas will escape with a lot of force, causing the balloon to pop.
• Boyle’s law states that for a fixed amount of gas at a constant temperature, the volume of the gas increases its pressure decreases. Likewise, the volume of a gas decreases as its pressure increases.
• Boyle’s law can be expressed mathematically as:
  (pressure 1)(volume 1) = (pressure 2)(volume 2) ,
  or P 1V 1 = P 2V 2

EXAMPLE

Boyle’s Law The gas in a balloon has a volume of
7.5 L at 100 kPa. The balloon is released into the atmosphere, and the gas expands to a volume of
11 L. Assuming a constant temperature, what is the pressure on the balloon at the new volume?

. List the given and unknown values.
Given: V 1 = 7.5 L
P 1 = 100 kPa
V 2 = 11 L
Unknown: P 2

Write the equation for Boyle’s law, and rearrange the equation to solve for P 2.
P 1V 1 = P 2V 2

P 2 = (P 1)(V 1)/V 2 = (100kPa)(7.5 L)/11L = 68kPa

• Charles’s law states that for a fixed amount of gas at a constant pressure, the volume of the gas increases as its temperature decreases. Likewise, the volume of a gas decreases as its temperature increases.
• As shown below, if the gas in an inflated balloon is cooled (at constant pressure), the gas will decrease in volume and cause the balloon to deflate.

• Gay-Lussac’s law states that the pressure of a gas increases as the temperature increases if the volume of the gas does not change.

This is why, if a pressurized container that holds gas, such as a spray can, is heated, it may explode.