Thermal Physics

Question 1

What is 0°C in Kelvin?

Answer 1

273.15K

Question 2

How do you calculate internal energy?

Answer 2

Internal energy = Σkinetic energies + Σpotential energies
ΔU = ΔQ - ΔW

Question 3

Describe thermal equilibrium?

Answer 3

When there is no net transfer of thermal energy between objects.

Question 4

What is the 1st Law of Thermodynamics?

Answer 4

The change of internal energy of an object is equal to the difference in energy transfer between heating and work done

Question 5

What is specific heat capacity, c?

Answer 5

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

Question 6

How can you calculate heat energy transferred in an object?

Answer 6

ΔQ = mcΔT

Question 7

What is continuous flow heating?

Answer 7

The process of heating a fluid by letting it flow continuously over a heater.

Question 8

How do you calculate power of a continuous flow heater?

Answer 8

P = mcΔT / t

Question 9

What three things are characteristics of the solid phase?

Answer 9

Molecules have little kinetic energy and so don’t move.
Solids maintain their shape, constant volume.
They cannot be easily compressed.

Question 10

What three things are characteristics of the liquid phase?

Answer 10

Molecules have some kinetic energy and are able to slide over one another.
Liquids flow and take the shape of their container.
They cannot be compressed.

Question 11

What three things are characteristics of the gas phase?

Answer 11

Molecules are far apart with lots of kinetic energy allowing them to move freely in space.
Gases take the volume of a container.
They can be easily compressed.

Question 12

Describe the relationship between the temperature of a pure substance and the energy supplied to it as it changes from solid to gas.

Answer 12

Temperature rises proportionally to the energy supplied.
At a definite temperature the substance will change phase at constant temperature.
Once the material has changed phase the temperature will be begin to rise again.

Question 13

What is the latent heat of a substance?

Answer 13

The energy needed to make a substance change phase.

Question 14

What is pressure?

Answer 14

The force per unit area a gas exerts normally to surfaces.

Question 15

What is Boyle’s Law?

Answer 15

The pressure of a given mass of an ideal gas is inversely proportional to its volume at a constant temperature.
P ∝ 1/V

Question 16

What is Charles’ Law?

Answer 16

The volume of an ideal gas at constant pressure is directly proportional to the absolute temperature.
V ∝ T.

Question 17

How do you calculate the work done in compressing a gas?

Answer 17

W = pΔV

Question 18

What is the Pressure - Temperature Law?

Answer 18

The pressure of an ideal gas at a constant volume is proportional to the absolute temperature.
p ∝ T

Question 19

What is an ideal gas?

Answer 19

A real gas that behaves in a way that can be modelled by Boyle’s Law.
Particles can be thought as taking up no volume.
There are no significant forces between particles.
The motion of particles is random.

Question 20

What is Avogadro’s Law?

Answer 20

The volume of two ideal gases at the same temperature must contain the same number of particles.

Question 21

What is the molar mass of a substance?

Answer 21

The mass of 1 mol of a substance. (kg/mol)

Question 22

What equation uses Boltzman’s constant?

Answer 22

pV = NkT
For N molecules of gas.

Question 23

What equation uses the molar gas constant?

Answer 23

pV = nRT
For n moles of gas.

Question 24

Explain how increasing temperature, increases pressure?

Answer 24

Increased temperature, increases KE of particles.
Increased KE means increased velocity and ∴ greater change in momentum.
This means greater forces and ∴ increased pressure.

Question 25

How does decreasing volume increase pressure?

Answer 25

Decreasing volume decreases distance between walls.
∴ increasing the frequency of particle collisions.
This increases the pressure.

Question 26

What 5 assumptions do ideal gases follow? Hint RAVED

Answer 26

Random motion of particles
Attraction - non between particles
Volume - can be though of as negligible
Elastic collisions
Duration of collisions is negligible

Question 27

What is Brownian motion?

Answer 27

The idea that small (solid) objects move randomly in fluids.
This is due to the random bombardment of molecules in the fluid.
This movement is slightly more on one side so the object is pushed by a force in an instant as the net forces shift direction.
This random motion gives evidence to the existence of atoms.

Question 28

What is internal energy?

Answer 28

The sum of the kinetic energy and potential energy of particles in an object.