Topic 3: Thermal Energy

Question 1

Temperature

Answer 1

A measurement of average kinetic energy of the molecules in a substance. A scalar quantity. If two objects have the same temperature, there will be no net heat flow between them (they are at thermal equilibrium).

Question 2

Internal energy

Answer 2

The energy contained in an object due to the random KE and PE of the molecules.

Question 3

Thermal energy

Answer 3

The non-mechanical transfer of energy between a system and its surroundings.

Question 4

Mole

Answer 4

The amount of a substance that contains the same number of particles as there are atoms in 12g of carbon-12.

Question 5

Molar mass

Answer 5

The mass of 1 mole of a substance. eg molar mass of water is 18g

Question 6

Avogadro’s constant

Answer 6

The number of particles in a mole. A=6.02 x 10^23

Question 7

Thermal capacity

Answer 7

The amount of thermal energy required to raise the temperature of an object by 1K.

Question 8

Specific heat capacity

Answer 8

The amount of thermal energy required to raise the temperature of 1kg of a substance by 1K.

Question 9

Macroscopic

Answer 9

Considers properties of matter such as pressure, volume, temperature (not in terms of particles).

Question 10

Microscopic

Answer 10

Considers properties of matter at a particle level. Molecules are in motion and collide with each other and the container.

Question 11

Kinetic energy of particles

Answer 11

Temperature is a measure of the average random kinetic energy of the particles.

Question 12

Evaporation

Answer 12

The process by which faster-moving molecules escape from the surface of a liquid. This results in a cooling of the liquid.

Question 13

Boiling

Answer 13

The process by which a liquid changes into a gas at the constant temperature of the boiling point.

Question 14

Specific latent heat

Answer 14

The amount of thermal energy required to change the state of 1kg of a substance without a change in temperature. SLH of fusion is solid to liquid; SLH of vaporisation is liquid to gas.

Question 15

Ideal gas

Answer 15

One that follows the gas laws for all values of P, V and T. PV= nRT

Question 16

Kinetic model of ideal gas

Answer 16

A model which treats a gas as many molecules subject to the following assumptions:
● The molecules obey Newton’s laws
● The intermolecular forces are negligible
● The molecules are spherical with negligible volume
● The motion of the molecules is random.
● The collisions are perfectly elastic.
● The time taken for a collision is negligible.

Question 17

Phases of matter

Answer 17

Particles in a solid are locked into the crystal structure and do not have enough KE to escape. In a liquid, they overcome the chemical bonds but cannot separate completely for the other atoms. The particles in a gas have enough KE to escape from each other.

Question 18

Thermal contact

Answer 18

For 2 objects, if thermal energy can be transferred as a result of temperature difference.

Question 19

Thermal equilibrium

Answer 19

2 objects at same temperature after thermal contact