Thermal Physics P2

Question 1

What is the temperature of a gas directly proportional to?

Answer 1

The average kinetic energy of its particles

Question 2

What is pressure?

Answer 2

The amount of force that an object exerts per unit area

Question 3

Why do gases exert a pressure on the walls of their container?

Answer 3

Gas particles have momentum and once they collide with a wall their momentum changes. This change suggests they exert a force on the wall which explains how they exert a pressure as pressure is force per unit area.

Question 4

What is a mole?

Answer 4

1 mole of a thing is 6.02 x 10^23 of that thing

Question 5

What is the molar mass?

Answer 5

The mass of one mole of a substance

Question 6

What is molecular mass?

Answer 6

The mass of one molecule of a substance

Question 7

What is the pressure law?

Answer 7

For any gas of fixed mass and volume, the pressure is proportional to temperature when measured in kelvin

Question 8

What is Charles’ law?

Answer 8

For any gas of fixed mass and pressure, the volume is proportional to the temperature in kelvin

Question 9

What is Boyle’s law?

Answer 9

For any gas of fixed mass and temperature, the volume is inversely proportional to the pressure

Question 10

What is Avogadro’s law?

Answer 10

For any gas of fixed pressure and temperature, the volume is proportional to its moles. Also the volume of 1 mole of gas is same for pretty much all gases

Question 11

What are the four main reasons why the gas laws break down for real gases?

Answer 11

Real gases can change state, occupy some volume, experience intermolecular forces and collide inelastically

Question 12

What are the four criteria required for a gas to be an ideal gas?

Answer 12

Never changes state, occupies no volume, has no intermolecular forces and collides elastically with one and other and the walls of the container

Question 13

What are the three reasons for using ideal gases?

Answer 13

They help us to understand real gases, they make the maths easier and most common gases behave closely to ideal gases at non-extreme temperatures and pressures

Question 14

What happens to the gas during expansion and compression?

Answer 14

During expansion there is work done by the gas and during compression there is work done on the gas

Question 15

When the pressure is constant, work done is given by:

Answer 15

W = p x change in volume

Question 16

How do you find the magnitude of the work done from a p-V graph?

Answer 16

Find the area below the graph

Question 17

What are the six assumptions that are made for the Kinetic Theory of Gases?

Answer 17

Gases are made up of small particles called molecules where their volume is negligible compared to the volume occupied by the whole gas.

Molecules are continuously moving in random directions and there is no intermolecular forces between molecules therefore they move in a straight line.

They collide with each other and the walls elastically and the time a molecule spends in collisions is negligible compared to the time it spends between collisions.

Question 18

How do you find the root mean square speed?

Answer 18

Square all of the speeds of the molecules, divide by the number of molecules and then square root the answer.

Question 19

What are two pieces of evidence which backs up the kinetic theory of gases?

Answer 19

We can derive the ideal gas equation from the kinetic theory equation which provides experimental support.

Brownian motion in smoke particles where air molecules move at random and knock into smoke particles provides evidence of random motion.

Question 20

How does the kinetic theory of gases explain the pressure law?

Answer 20

When temperature increases molecules move faster therefore more frequent collisions.

This increases the force on the walls as there is a greater change in momentum therefore the pressure increases.

Question 21

What is heating?

Answer 21

energy transfer due to a temperature difference

Question 22

What is thermal equilibrium?

Answer 22

when two objects are at the same temperature therefore heating doesn’t occur

Question 23

What is temperature?

Answer 23

measure of the average kinetic energy of the particles

Question 24

What is the Celsius and Kelvin scale based off?

Answer 24

Celsius is based off of water and the Kelvin scale is based off the average kinetic energy of particles

Question 25

What is internal energy?

Answer 25

Sum of the randomly distributed kinetic and potential energies of its particles

Question 26

What is thermal energy?

Answer 26

Sum of the randomly distributed kinetic energies of an objects particles

Question 27

What is the change in internal energy equal to?

Answer 27

the energy transfer due to heating + the work done on the system (or - work done by the system)

Question 28

What is specific heat capacity?

Answer 28

The amount of energy required to raise the temperature of 1kg of a substance by 1K (Without changing its state)

Question 29

What is latent heat?

Answer 29

Energy transferred during a change of state without changing the temperature

Question 30

What is the specific latent heat of fusion?

Answer 30

Energy required to change 1kg of material from solid to liquid without a change of temperature

Question 31

What is the specific latent heat of vaporisation?

Answer 31

Energy required to change 1kg of material from liquid to gas without a change of temperature

Question 32

How do you find the molecular mass of a substance?

Answer 32

Divide the molar mass by Avogadro’s constant

Question 33

Why are the ideal gas laws empirical laws?

Answer 33

Because they are based on observations and experiments

Question 34

How do you find the internal energy of a gas?

Answer 34

The average kinetic energy of the particles multiplied by the number of particles (3/2pV)