1. Gas Law Kinetic Theory of Gases

2. Gas in closed container Number of molecules is constant Mass of gas is constant Behavior of the gas depends on properties of gas

3. Properties of Gas Volume Molecules move freely and fill the whole space Gas volume = container volume Temperature Average kinetic energy of molecules is proportional to the temperature

4. Properties of Gas (cont) Pressure When the molecules collide and bounce back, there is a change in momentum Force is exerted on the wall Force per unit area is the pressure of the gas

5. Relationship Between Pressure and Volume When the volume decrease, the number of molecules per unit volume increases. Same number of molecules will move in a smaller space Molecules collide more frequently with the walls of container. Thus, pressure will increase

6. Boyle’s Law For a fixed mass of gas, the pressure of the gas is inversely proportional to its volume when the temperature is kept constant. P α 1/V PV = constant P1V1 = P2V2

7. Example The air in a syringe has an initial volume of 12.0 cm3 and pressure of 100 kPa. The nozzle of the syringe is closed and the piston is pushed inwards until the volume of the air becomes 7.5 cm3. What is the pressure of the compressed air in the syringe?

8. Solution P1 = 100 kPa V1 = 12.0 cm3 P2 = final pressure V2 = 7.5 cm3 Using Boyle’s law, P1V1 = P2V2 P2 = P1V1/ V2 P2 = (100 × 12.0) / 7.5 P2 = 160 kPa