3.3 PARTICLE MODEL + PRESSURE

Question 1

Describe the motion of molecules in a gas.

Answer 1

They are in constant random motion.

Question 2

What factor affects the average kinetic energy of gas molecules?

Answer 2

● The temperature of the substance
● The higher the temperature, the higher
the average kinetic energy of the molecules

Question 3

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

Answer 3

Pressure of the gas will increase as the temperature increases.

Question 4

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

Answer 4

● Kinetic energy of molecules increases ● Collisions between molecules becomes
more frequent
● Greater rate of change of momentum
● Greater force and therefore pressure

Question 5

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?

Answer 5

● There are more collisions per second in gas B than in gas A
● The rate of collisions is higher in B

Question 6

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

Answer 6

● The net force acts at right-angles to the container’s surface
● The force increases as pressure increases

Question 7

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

Answer 7

● 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

Question 8

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

Answer 8

It is constant. p V = constant

Question 9

What is the unit used for pressure?

Answer 9

Pascal (Pa)

Question 10

What increases when you do work on a gas?

Answer 10

● The internal energy of the gas
● This can also lead to an increase of
temperature

Question 11

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

Answer 11

● 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