Thermal Physics

Question 1

Internal energy

Answer 1

The sum of all the kinetic energies and potential energies of all its particles.

Question 2

How can internal energy be increased?

Answer 2

-Do work on the system to transfer energy to it.
-Increase the temperature of the system.

Question 3

What happens when the state of a substance changes?

Answer 3

Its internal energy also changes because the potential energy of the system changes while the kinetic energy is kept constant.

Question 4

Specific heat capacity

Answer 4

The amount of energy required to increase the temperature of 1kg of a substance by 1 degrees/1K without changing its state.

Question 5

Specific latent heat

Answer 5

The amount of energy required to change the state of 1kg of material without changing its temperature.

Question 6

What are the two types of specific latent heat?

Answer 6

-Specific latent heat of fusion
-Soecific latent heat of vaporisation

Question 7

What do the gas laws describe?

Answer 7

They describe the experimental relationship between pressure, volume and temperature for a fixed mass of gas.

Question 8

What are the gas laws?

Answer 8

They are empirical in nature so they are based on observation and experimental evidence.

Question 9

Boyle’s law

Answer 9

When temperature is constant, pressure and volume are inversely proportional.

Question 10

Charles’ law

Answer 10

When pressure is constant, volume is directly proportional to absolute temperature.

Question 11

Pressure law

Answer 11

When volume is constant, pressure is directly proportional to absoulute temperature.

Question 12

Absolute 0

Answer 12

-273 degrees or 0K. Lowest possible temperature and is the temp at which particles have no kinectic energy and the volume and pressure of gas are 0

Question 13

1 mole of a substance

Answer 13

Equal to 6.02x10^23 atoms. Can conver by multiplying the num of moles by 6.02x10^23 which is Avogadro’s constant.

Question 14

Molar mass

Answer 14

The mass of one mole of a substance and can be found by finding the relative molecular mass.

Question 15

What is done to change a gas’ volume?

Answer 15

Work is done to change its volume when it is at a constant pressure.

Question 16

Brownian motion

Answer 16

The random motion of large particles in a fluid caused by collisions with surrounding particles. Evidence for the existence of atoms and molecules.

Question 17

Explain Boyle’s law

Answer 17

• Pressure is inversely proportional to volume at constant temperature E.g If you increase the volume of a fixed mass of gas, its molecules will move further apart so collisions will be less frequent therefore pressure decreases.

Question 18

Explain Charle’s law

Answer 18

Volume is directly proportional to temperature at constant pressure. When the temperature of a gas is increased, its molecules gain kinetic energy meaning they will move more quickly and because pressure is kept constant (therefore frequency of collisions is constant) the molecules move further apart and volume is increased.

Question 19

Explain the Pressure law

Answer 19

Pressure is directly proportional to temperature at constant volume. When the temperature of a gas is increased, its molecules gain kinetic energy meaning
they will move more quickly, as volume is constant the frequency of collisions between molecules and their container increases and they collide at higher speeds therefore pressure is increased.

Question 20

Kinetic theory model

Answer 20

An equation which relates several features of a fixed mass of gas, including its pressure, volume and mean kinetic energy.

Question 21

Assumptions with the kinetic theory model.

Answer 21

-No intermolecular forces act on the molecules.
-The duration of collisions is negligible in comparison to time between collisions.
-The motion of molecules is random, and they experience perfectly elastic collisions.
-The motion of the molecules follows Newton’s laws.
-The molecules move in straight lines between collisions.