Gas Laws Kinetic Theory F.4 Physics Lectures Gas Laws Kinetic Theory

Boyle’s Law The following apparatus is used to investigate how the pressure of a fixed mass of air varies with its volume when the temperature is kept constant.

Procedure Pressure is increased by applying the foot-pump Volume of air is read from the scale Pressure is measured by a Bourdon gauge Several pairs of readings of pressure and volume are taken

Result

Graph Plotting

Conclusion P  1/V PV = constant P1V1 = P2V2 Boyle’s Law Pressure of a fixed mass of gas at constant temperature is inversely proportional to its volume

Charle’s Law

Procedure An air column is trapped in a capillary tube. It is heated up in a water bath in stages. The thermometer reading is taken. The length of the air column is measured. The reading are taken only after they have remained steady.

Result

Graph Plotting

Conclusion V  T V/T = constant V1 /T1 = V2/T2 Charle’s Law Volume of a fixed mass of gas at constant pressure is directly proportional to its Kelvin temperature.

Pressure Law

Procedure: Air trapped in a flask is heated in a water bath. Use the thermometer and Bourdon gauge to measure the temperature and the pressure of the air. Take about several readings with different temperature.

Result

Graph Plotting

Conclusion P  T P/T = constant P1 /T1 = P2/T2 Pressure Law Pressure of a fixed mass of gas at constant volume is directly proportional to its Kelvin temperature.

General Gas Equation Boyle’s Law: PV = constant Charle’s Law: V/T = constant Pressure Law: P/T = constant PV/T = constant

Kinetic Theory All matter is made up of particles, called molecules. They are constantly in motion. When they are close together, the molecules attract each other strongly. When they are far apart, they hardly attract each other.

Solids The particles are close together. They are held together by strong forces. They vibrate to and fro, but cannot change positions. They have a fixed volume and shape.

Liquid The particles are close together. They vibrate so vigorously that the forces can no longer hold them in fixed position. They have a fixed volume but no fixed shape.

Gas The particles are very far apart and hardly attract each other. They move at random at very high speeds. They have no fixed volume and shape.

Brownian Motion A smoke particle is bombarded by millions of air molecules around it. The bombardment comes from all sides but not in equal number. Brownian motion provides evidence for particle motion. This can be explained by using the kinetic theory.

Kinetic theory and Boyle’s Law When a gas is compressed, the molecules have less volume to move in. They hit the walls more often and so produce a greater pressure.

Kinetic theory and Charles’ Law As temperature rises, the molecules move faster and hit the walls more often. If the pressure is to remain constant, the volume must increase.

Kinetic theory and Pressure Law As temperature rises, the molecules move faster. When the volume is fixed, the molecules hit the walls more often. This increases the pressure.