P3 - Particle Model of Matter 3

Question 1

Describe the motion of molecules in a gas

Answer 1

They are constant in a random motion

Question 2

What factor affects the average kintetic 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 become 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 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