Thermal Physics

Question 1

Thermal equilibrium

Answer 1

If two substances are in contact at different temps, there will be a net flow of thermal energy from the hotter object to the cooler object, and once at the same temperature they will be in thermal equilibrium (no net energy transfer between them)

Question 2

Kinetic model of a solid

Answer 2

• atoms closely packed together
• strong electrostatic forces of attraction
• negative electrostatic potential energy (force required to separate)
• molecules have KE, and vibrate around their fixed positions

Question 3

Kinetic model of a liquid

Answer 3

• greater mean separation than a solid
• more KE than a solid, able to move around (and around/over each other)
• weaker electrostatic attraction
• less negative electrostatic potential energy

Question 4

Kinetic model of a gas

Answer 4

• highest KE, allowing them to move freely and rapidly, colliding elastically with each other
• moves with random velocity and direction
• electrostatic forces of attraction are negligible
• maximum electrostatic potential energy (0J)

Question 5

Brownian motion

Answer 5

Molecules travel in random directions with random velocity, and can be seen by looking at smoke particles in air as they collide with air particles and momentum is transferred in random ways.

Question 6

Internal energy

Answer 6

Sum of the randomly distributed kinetic and potential energies of the substance

Question 7

PE/KE change with temperature and stats

Answer 7

KE increases with increase in temp, and stays the same during change of state

PE increases with change of state, and stays the same during increase in temp

Temperature of the substance will stay the same while changing phase as the thermal energy is used to overcome electrostatic bonds between molecules

Question 8

Absolute zero

Answer 8

0K, when molecules stop moving entirely. Substance has minimal internal energy, only from the electrostatic potential energy (0 KE)

Question 9

Specific heat capacity definition

Answer 9

The energy required per unit mass to increase the temperature by 1K

E=mcx(changeintemp)

Question 10

Determining SHC (method of mixtures)

Answer 10

Question 11

Specific latent heat

Answer 11

Energy required per unit mass to change the state of a substance from solid to liquid (fusion) or liquid to gas (vaporisation)

E = mL (L is the SLH)

Question 12

Determining SHL

Answer 12

Similar set up to determining SHC, but the time when temperature is constant is found and energy transferred is found (W=Pt)

Question 13

One mole

Answer 13

The amount of substance containing 6.02x10^23 particles

Question 14

Determining number of particles in a substance equation

Answer 14

number of moles = mass of substance / molar mass (nucleon number)

Question 15

5 assumptions of an ideal gas

Answer 15

• gas contains a large number of atoms moving with random, rapid motion (brownian)
• volume of gas atoms negligible when compared to total volume of gas
• all collisions are perfectly elastic
• time taken for atoms to collide is negligible compared to time between collisions
• electrostatic forces between atoms are negligible, except for when atoms are colliding

Question 16

Explain pressure using the kinetic theory of gases

Answer 16

Question 17

Ideal gas laws (Boyle and Charles)

Answer 17

Question 18

Investigating Boyle’s law

Answer 18

Question 19

Estimating absolute zero using gas

Answer 19

Question 20

Root mean square speed

Answer 20

Question 21

Boltzmann distribution

Answer 21

Question 22

Mean KE and temperature

Answer 22

Question 23

Internal energy of an ideal gas

Answer 23

Question 24

Specific latent heat of fusion of ice experiment

Answer 24

Place a funnel over a beaker, with filter paper in the bottom. Fill funnel with ice and place heater in the ice with a clamp stand. Energy supplied to the ice can be found using W = VIt, and the mass of the melted ice can be found with a mass balance that the beaker sits on. Using E=mL, latent heat of fusion can be found by plotting change in mass against time, the gradient being VI/L. The ice must be at the point of melting before the time is recorded and the temperature of the ice shouldn’t change.