T3 particle model and pressure

Question 1

describe the motion of molecules in a gas

Answer 1

they are in constant random motion

Question 2

what factor affect the average kinetic energy of gas molecules

Answer 2

• 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 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
• 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
• 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
• 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