No Longer On Exam

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 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 and wall of container becomes more frequent.
• Greater rate of change of momentum.
• Greater force exerted on wall of container and therefore pressure increases.

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 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 between molecules and the walls of a container.
• 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 (higher average KE).

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.