4.3.3 - Particle Model and Pressure

Particle Model of Matter

Describe the motion of molecules in a gas.

They are in constant random motion

What factors affect 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 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 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, resulting in a lower pressure

What can be said about the product of pressure and volume for a fixed mass of gas at a constant temperature? (Higher)

It is constant

p V = constant

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