3.3 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 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

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

Answer 3

• 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 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 3

what is the unit used for pressure?

Answer 3

pascal (Pa)

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

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

Answer 5

• the net force acts as right-angles to the container’s surface
• the force increases as pressure increases

Question 5

what increases when you do work on a gas?

Answer 5

• the internal energy of the gas
• this can also lead to an increase of temperature

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 5

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

Answer 5

• 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

Question 6

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

Answer 6

it is constant.
p V = constant