Particle Model and Pressure

Describe the motion of molecules in a gas.

They are in constant random motion.

What factor affects the average kinetic energy of gas molecules?

• The temperature of the substance

•  The higher the temperature, the higher the average kinetic energy of the molecules

What effect does increasing temperature have on the pressure of a gas when held at constant volume?

Pressure of the gas will increase as the temperature increases.

Why does pressure increase as temperature increases (at a constant volume)?

• Kinetic energy of molecules increases

• Collisions between molecules becomes more frequent

•  Greater rate of change of momentum

• Greater force and therefore pressure

If gas A is at a low pressure, and gas B is at a high pressure, what can be said about the rate of collisions in each gas?

• There are more collisions per second in gas B than in gas A

•  The rate of collisions is higher in B

Describe the force that the pressure of a gas exerts on the walls of its container.

• The net force acts at right-angles to the container’s surface

•  The force increases as pressure increases

Explain how increasing the volume of a gas results in a decrease of pressure.

• Molecules become more spread out and so time between collisions increases

• This reduces the rate of collisions

• Rate of change of momentum decreases, and so force exerted on container decreases, resulting in a lower pressure

What is the unit used for pressure?

Pascal (Pa)

What increases when you do work on a gas?

• The internal energy of the gas

• This can also lead to an increase of temperature

Why does the temperature of air inside a bike pump increase when it is pumped?

• Work is done on a gas when it is compressed

• Doing work on a gas increases its internal energy, so also increases the average kinetic energy of the molecules

• Temperature increases with an increase of average kinetic energy