Gases have unique properties. Some important properties of gases are listed below.

• 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.

Chapter 14 Section 3 Behavior of Gases

Important Properties of Gases, continued

• 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 – these collisions create pressure


Properties of Gases, continued

• 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.


Factors that Affect Gas Pressure - include its temperature, its volume, and the number of particles within it.

TEMPERATURE• Raising the temperature of a gas will increase its

pressure if the volume of the gas and the number of particles are constant.

• Increasing the speed of the particles but keeping the space available to move the same causes the number of collisions to increase.

• This is visible when the gas in tires heats up due to highway or NASCAR driving, potentially causing the tire to explode due to increased pressure.

Section 3 Behavior of GasesChapter 14

VOLUME

• Reducing the volume of a gas increases its pressure if the temperature of the gas and the number of particles in the gas remain constant.

• The gas moves at the same speed but within the confines of a smaller space causing a greater number of collisions.

• The pressure – volume relationship of gases allows inhaling and exhaling in our breathing process to occur.


NUMBER OF PARTICLES

• Increasing the number of particles will increase the pressure of a gas if the temperature and the volume are constant.

• Adding more air into inflated tires becomes increasingly difficult to impossible after the tire’s internal pressure is at maximum.


Gas Laws

• 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:(pressure1)(volume1) = (pressure2)(volume2) ,or P1V1 = P2V2


Math Skills

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?


Gas Laws, continued• Charles’s law states that for a fixed amount of gas at

a constant pressure, the volume of the gas increases as its temperature increases. Likewise, the volume of a gas decreases as its temperature decreases.

• 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.


Gas Laws, continued

• The equation for Charles’s law is

V1 = V2, the volume of a gas is directly

T1 T2 proportional to its absolute temperature

• Absolute temperature is the Kelvin temperature.

K = oC + 273.15 There are no values below

zero on this scale.


Gas Laws, continued

• 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.


Gas Laws, continued

The Combined Gas Law• The relationships described in Boyle’s law, Charles’s

law, and Gay-Lussac’s laws can be summarized into one law. This is the combined gas law.

• The equation for the combined gas law is

P1. V1 = P2 . V2

T1 T2

• Recall that temperature must be in the Kelvin scale.


Gas Laws, continued

Problem: A cylinder that contains air at a pressure of 100 kPa has a volume of 0.75 L. The pressure is increased to 300 kPa. The temperature does not change. Find its new volume of air.

Solution: • Initial pressure = 100 kPa, Initial volume = 0.75 kPa• Final pressure = 300 kPa, Final volume = unknown• Temperature is unchanged.


• Adjust the combined gas law formula by omitting the temperatures leaving - P1V1 = P2V2

• Solve for the unknown variable, leaving –

V2 = P1V1

P2

• Replace variables with numbers and solve the unit:

V2 = (100 kPa)(0.75 L) = 0.25 L

300 kPa• Check answer for credibility.


Gases have unique properties. Some important properties of gases are listed below.

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