Gas LawKinetic Theory of Gases

Gas in closed containerNumber of molecules is constantMass of gas is constantBehavior of the gas depends on properties of gas

Properties of GasVolumeMolecules move freely and fill the whole spaceGas volume = container volumeTemperatureAverage kinetic energy of molecules is proportional to the temperature

Properties of Gas (cont)PressureWhen the molecules collide and bounce back, there is a change in momentumForce is exerted on the wallForce per unit area is the pressure of the gas

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

Boyle’s LawFor 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

ExampleThe 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?

SolutionP1 = 100 kPaV1 = 12.0 cm3P2 = final pressureV2 = 7.5 cm3Using Boyle’s law,P1V1 = P2V2P2 = P1V1/ V2P2 = (100 × 12.0) / 7.5P2 = 160 kPa