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

1. Section 3 Behavior of Gases Chapter 14 • 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.

2. Section 3 Behavior of Gases Chapter 14 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

3. Section 3 Behavior of Gases Chapter 14 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.

4. Section 3 Behavior of Gases Chapter 14 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.

5. Section 3 Behavior of Gases Chapter 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.

6. Section 3 Behavior of Gases Chapter 14 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.

7. Section 3 Behavior of Gases Chapter 14 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

8. Section 3 Behavior of Gases Chapter 14 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?

9. Section 3 Behavior of Gases Chapter 14 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.

10. Section 3 Behavior of Gases Chapter 14 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.

11. Section 3 Behavior of Gases Chapter 14 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.

12. Section 3 Behavior of Gases Chapter 14 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.

13. Section 3 Behavior of Gases Chapter 14 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.

14. Section 3 Behavior of Gases Chapter 14 • 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.