Thermal Physics

Question 1

Thermal equilibrium

Answer 1

No net heat flow between objects

Question 2

Pressure

Answer 2

The force applied perpendicular to the surface of an object, per unit area.

Question 3

Internal energy

Answer 3

The sum of the total kinetic energy and potential energy associated with the atoms/molecules of a system

Question 4

Specific heat capacity

Answer 4

The heat energy required to raise the temperature of 1kg of a substance by 1 degree Kelvin.

Question 5

Specific latent heat of fusion

Answer 5

The energy absorbed by 1kg of a substance to change its state from solid to liquid with no change in temperature

Question 6

Specific latent heat of vaporisation

Answer 6

The energy absorbed by 1kg of a substance to change its state from liquid to gas with no change in temperature

Question 7

Boyle’s law

Answer 7

For a fixed mass of gas at a constant temperature the product of pressure and volume is a constant.

Question 8

Assumptions of an Ideal Gas

Answer 8

Collisions between molecules and the container walls are elastic.
Force between molecules is negligible except during collisions.
Time within a collision is negligible compared to time between collisions.
Volume occupied by particles is negligible compared to the volume of the container.

Question 9

1 mole of a substance…

Answer 9

…contains 6.02x10^23 particles

Question 10

How does a gas exert a pressure on a container wall?

Answer 10

Momentum of the molecule changes when it collides with the wall.
Force on the molecule is the rate of change of momentum (by Newton’s 2nd law).
Force on the wall is equal but opposite to the force on the molecule (by Newton’s 3rd law).
Pressure is force per unit area.

Question 11

Brownian motion

Answer 11

Random motion (of smoke particles etc) due to many collisions with very fast, tiny (unseen) molecules which are moving in random directions.

Question 12

Avogadro’s Constant

Answer 12

6.02x10^23 - the number of particles in a system when there is 1 mole present.

Question 13

What does E = mcΔθ stand for?

Answer 13

E is the supplied energy to the substance
m is the mass of the substance
c is the specific heat capacity of the substance
Δθ is the temperature change

Question 14

What do θ and T stand for?

Answer 14

θ is the symbol for temperature on the Celsius scale (units: ‘degrees celsius’)
T is the symbol for temperature on the thermodynamic scale (units: ‘degrees kelvin’)

Question 15

What does pV = NkT mean?

Answer 15

p is pressure
V is volume
N is number of particles
k is Boltzmann constant (1.38x10^-23)
T is temperature in kelvin

Question 16

What does pV = nRT mean?

Answer 16

p is pressure
V is volume
n is number of moles of gas
R is the molar gas constant (8.31)
T is temperature in kelvin

Question 17

What does E = (3/2)kT mean?

Answer 17

E is the mean translational kinetic energy of atoms
k is Boltzmann constant (1.38x10^-23)
T is temperature in kelvin

Question 18

How are k and R related?

Answer 18

Molar gas constant = Boltzmann constant * Avogadro constant