Chapter 14 Thermal Physics

Question 1

What is a triple point?

Answer 1

This is a specific temperature and pressure where a substance can be a solid or a liquid or a gas and exist in a thermal equilibrium. For water this means that the ice doesn’t melt, the water vapour doesn’t condense

Question 2

What happens if a hot object is placed next to a cold object?

Answer 2

The net flow of heat is from the hot object to the colder object.

Question 3

What is thermal equilibrium?

Answer 3

This is when there is no net flow of thermal energy between them so all the objects must be at the same temperature

Question 4

How is a scale of temperature created?

Answer 4

Two points are defined and then the temperature of other objects can be positioned on this scale

Question 5

What is the absolute temperature scale?

Answer 5

This is a scale where the two defined points are the triple point of water and the lowest possible temperature (absolute 0).

Question 6

What is the SI unit for Absolute temperature?

Answer 6

Kelvin (K)

Question 7

What is an increase of 1*K in Celsius?

Answer 7

Increase of 1*C

Question 8

What is 0*C in kelvin?

Answer 8

273*K

Question 9

What is the density of ice vs water?

Answer 9

Ice is less dense than water. This is very uniquie

Question 10

What happens to atoms/molecules in a solid?

Answer 10

They pack together tightly because of strong electrostatic forces. All the atoms / molecules stay together in a fixed formation

Question 11

What happens to the atoms/molecules in a liquid?

Answer 11

They are still close together but they can move further apart and can change position

Question 12

What happens to the atoms/molecules in a gas?

Answer 12

The atoms / molecules are free to move apart and there is almost no forces of attraction between them. They move randomely

Question 13

What does the spacing of molecules in a substance at different physical phases affect?

Answer 13

It affects the density

Question 14

Why is water less dense as a solid?

Answer 14

Because it forms a regular crystalline structure

Question 15

What is the density of a solid vs liquid (usually)?

Answer 15

Solids are far more dense

Question 16

What is the internal energy of a substance?

Answer 16

It is the sum of the randomly distributed kinetic and potential energies of atoms or molecules within a substance.

Question 17

What happens to the internal energy of a substance when it is heated and why?

Answer 17

The internal energy increases because more heat causes the kinetic energy of a substance to increase. The hotter a substance the more kinetic energy it has

Question 18

How can the internal energy of a substance increase without an increase in temperature?

Answer 18

If the substance is changing state. The energy is increased because the electrostatic forces between the atoms / molecules is increased

Question 19

What happens when a substance is heated so it starts to melt / vaporise?

Answer 19

The heat energy goes into breaking the electrostatic forces and not into kinetic energy. Once the forces have been broken, only then does the heat energy go into increasing the kinetic energy

Question 20

What is the electrostatic potential energy in a gas?

Answer 20

Zero

Question 21

What is the electrostatic potential energy in a liquid?

Answer 21

Negative

Question 22

What is the electrostatic potential energy in a solid?

Answer 22

Very large negative

Question 23

What is specific heat capacity?

Answer 23

It is the energy required to increase the temperature per unit of substance(1Kg) by 1*K

Question 24

What is the specific heat capacity of water? is this high or low?

Answer 24

4200JKg^-1K^-1

This is exceptionally high

Question 25

What is the equation to find the energy put into a substance?

Answer 25

E = mcΔθ
E = Energy
m = mass
c = Specific heat capacity
θ = temperature

Question 26

How is specific heat capacity calculated?

Answer 26

It is calculated by using an emersion heater placed in the substance which is surrounded by insulator material. The energy into the substance is calculated using a volt meter and an ammeter. They are used to find the joules of energy transferred.
A thermometer is used to measure the change in temperature
The mass of the substance is weighed at the beginning
Then use the equation: c = IVt / mΔθ

Question 27

What can the gradient of a temperature-time graph be used to calculate?

Answer 27

It can be used to calculate the specific heat capacity using the equation: c = Power / m x gradient

Question 28

What is the method of mixtures?

Answer 28

To work out the specific heat capacity, mix two substances together and record the final temperature. If the SHC of one of the substances is known then the other SHC can be calculated. Use the equation:
mcΔθ = mcΔθ

Question 29

What is specific latent heat?

Answer 29

This is the energy required to change the phase per unit of mass while at a constant temperature

Question 30

What is the equation for specific latent heat?

Answer 30

L = E / M

Question 31

What is the specific latent heat of fusion?

Answer 31

This is the specific latent heat when a solid turns to a liquid

Question 32

What is the specific latent heat of vaporisation

Answer 32

This is the specific latent heat when a liquid turns to a gas

Question 33

How is the specific latent heat of fusion measured and calculated?

Answer 33

By heating the solid version of a substance with a submersion heater and using E = IVt.
This is then divided by the amount of solid melted to get the specific latent heat

Question 34

How is the specific latent heat of vaporisation measured and calculated?

Answer 34

This is done by heating a liquid and collecting the gas and measuring the mass of the gas by condensing it.
These equations are used: E = IVt and L = E / M

Question 35

What are the conditions for standard values of specific heat capacity and specific latent heat for substances?

Answer 35

They are all at atmospheric temperatures

Question 36

When working out the energy into a substance that is increasing in temperature and changing states what needs to happen?

Answer 36

Both the specific heat capacity and the specific latent heats need to be calculated and added together