Thermal Physics definitions

Question 1

Absolute zero

Answer 1

the lowest possible temperature the temperature at which an object has minimum internal energy. The volume and pressure of an ideal gas would be zero at a temperature of absolute zero.

Question 2

Absolute temperature T

Answer 2

in kelvin = temperature in °C + 273(.15).

Question 3

Avogadro constant NA

Answer 3

the number of atoms in 12 g of carbon-12. Its value is 6.02 x 1023 mol -1.

Question 4

Boiling point

Answer 4

the temperature at which a pure liquid at atmospheric pressure boils.

Question 5

Boyle’s law:

Answer 5

for a fixed mass of gas at constant temperature, its pressure is inversely proportional to its volume.

Question 6

Brownian motion

Answer 6

the random and unpredictable motion of a particle such as a smoke particle caused by molecules of the surrounding substance colliding at random with the particle. Its discovery provided evidence for the existence of atoms.

Question 7

Charles’ law

Answer 7

for a fixed mass of an ideal gas at constant pressure, its volume is directly proportional to its absolute temperature.

Question 8

Energy

Answer 8

the capacity to do work.

Question 9

Heat Q

Answer 9

energy transfer due to a difference in temperature.

Question 10

Ideal gas

Answer 10

a gas under conditions such that it obeys Boyle’s law (and the ideal gas law pV = nRT). The interactions between the particles are negligible apart from during collisions, so they have no potential energy.

Question 11

Internal energy

Answer 11

of an object is the sum of the random distribution of the kinetic and potential energies of its molecules.

Question 12

Kinetic energy

Answer 12

the energy of a moving object due to its motion.

Question 13

Mean square speed

Answer 13

the mean value of the square of the molecular speeds of the molecules of a gas.

Question 14

Kinetic theory assumptions

Answer 14

1. Duration of collisions are negligible compared to the time between collisions; 2. The molecules move with random motion; 3. There are no interactions (forces) between the molecules except during collisions); 4. The volume of the molecules is negligible compared to the volume of the gas; 5. All collisions are elastic

Question 15

Melting point

Answer 15

the temperature at which a pure substance melts.

Question 16

Mole

Answer 16

one mole of a substance consisting of identical particles is the quantity of a substance that contains NA (6.02 x 1023 mol -1) particles of the substance.

Question 17

Molar mass

Answer 17

the mass of one mole of a substance.

Question 18

Pressure

Answer 18

the force per unit area that is exerted normally on a surface

Question 19

Pressure law

Answer 19

for a fixed mass of an ideal gas at constant volume, its pressure is directly proportional to its absolute temperature.

Question 20

Root mean square speed, crms:

Answer 20

square root of the mean value of the square of the molecular speeds of the molecules of a gas.

Question 21

Specific heat capacity c

Answer 21

the energy needed raise the temperature of 1 kg of the substance by 1 K without change of state.

Question 22

Specific latent heat of fusion

Answer 22

the energy needed to change the state of unit mass of a solid to a liquid without change of temperature

Question 23

Specific latent heat of vaporisation

Answer 23

the energy needed to change the state of unit mass of a liquid to a vapour without change of temperature

Question 24

Sublimation

Answer 24

the change of state when a solid changes to a vapour directly.

Question 25

Temperature

Answer 25

Temperature is proporional to the average translational kinetic energy of molecules in a substance. For an ideal gas they are related by: = 3/2 kT

Question 26

Thermal energy

Answer 26

the internal energy of an object due to temperature.

Question 27

Thermal equilibrium

Answer 27

when no overall heat transfer occurs between objects that are at the same temperature as each other. The mean kinetic energy of molecules in the objects will be the same.