Thermal Physics (topic 3)

Question 1

Heat

Answer 1

Transfer of energy between a system and its surroundings.
Q = heat (J)

Question 2

Temperature

Answer 2

Average kinetic energy of the molecules. Larger velocities -> larger Ek. Faster particles -> hotter
T = temperature (°C or K)

Question 3

Internal energy

Answer 3

Total kinetic energy plus potantial energy.
U = internal energy (J)

Question 4

Specific heat capacity

Answer 4

Energy needed to raise the temperature of one unit of mass of material by 1K

Q = mcΔT

where
Q = heat (J)
m = mass (kg)
c = specific heat capacity (J kg^-1 °C^-1)
ΔT = change in temperature (°C or K)

Heat gained = heat lost

Question 5

Specific latent heat

Answer 5

Energy per unit mass absorbed or released during a phase change.

Q = mL (use for every phase change)

where
Q = heat (J)
m = mass (kg)
L = specific latent heat (J kg^-1)

Question 6

Ideal gas

Answer 6

• No forces between molecules
• must work for all pressures volumes and temperatures

Question 7

Pressure

Answer 7

p = force / area

**If volume gets smaller, pressure increases

Question 8

Ideal gas law

Answer 8

pV = nRT

where
p = pressure (Pa)
V = volume (m^3)
n = number of moles
R = gas constant (J mol^-1 K^-1)
T = temperature (K)

Question 9

Gas laws

Answer 9

1. Constant volume
2. Charles’ law
3. Boyle’s law

Question 10

Constant volume

Answer 10

pV = nRT; v = constant
p is proportional to T. As temperature goes up, pressure goes up

In a graph: straight slope from the origin

Question 11

Charles’ law

Answer 11

pV = nRT; p = constant
V is proportional to T. As temperature goes up, volume goes up

In a graph: straight slope from the origin

Question 12

Boyle’s law

Answer 12

pV = nRT; T = constant
p is proportional to 1/V

In a graph: a negative exponential graph

Question 13

Moles and Avogadro

Answer 13

n = N / Na

where
n = number of moles
N = number of atoms
Na = Avogadro’s constant

Question 14

Power equation

Answer 14

P = ΔE / Δt

where,

P = power
ΔE = change in energy
Δt = change in time

Question 15

Kinetic model of an ideal gas

Answer 15

Intermolecular forces are negligible.

Therefore, a real gas may be approximated by that of an ideal gas under the following conditions as they all reduce effect of intermolecular forces.

• the gas density is low - gas particles are far apart
• pressure is low - gas particles are far apart
• temperature is high - gas particles move more quickly