Unit 6 Thermal Physics

Question 1

What is heat?

Answer 1

Heat is the total amount of energy of all the particles in a body.

Question 2

What is temperature?

Answer 2

Temperature is a measure of the average energy of a single particle in a body.

Question 3

What is thermal equilibrium?

Answer 3

A state where there is no net flow of heat (ie. thermal energy) between objects therefore all objects are at the same temperature.

Question 4

What happens when a substance is changing state?

Answer 4

Its temperature stays constant
The kinetic energy of its particles do not change
Its internal energy changes because the potential energy of its particles changes as the forces between them change and bonds between them are made or broken.

Question 5

Define specific heat capacity of a substance

Answer 5

The amount of energy needed to raise the temperature of 1 kg of the substance by 1 degree Celsius without a change of state

Question 6

Define specific latent heat of fusion

Answer 6

The amount of energy needed to change 1kg of it from solid to liquid without a change in temperature.

Question 7

Define specific latent heat vaporisation

Answer 7

The amount of energy need to change 1kg of it from liquid to gas without a change in temperature

Question 8

What is the zeroth law of Thermodynamics?

Answer 8

If two objects are in thermal equilibrium with a third object, then they are all in thermal equilibrium with each other (ie. no net flow of heat between all three objects, therefore they’re all at the same temperature.)

Question 9

What is the coldest possible temperature?

Answer 9

Absolute zero which is theorised at 0 kelvin, -273 degrees celsius,= or -460 degrees fahrenheit. A state where the substance has minimum internal energy.

Question 10

What forces determine potential energies of particles?

Answer 10

Attractive forces.

Question 11

Describe the potential energy of particles in the three states?

Answer 11

Solids - some potential energy
Liquid - less potential energy as smaller attractive forces
Gas - negligible potential energy

Question 12

What is potential energy?

Answer 12

Energy due to position.

Question 13

What is always smaller, potential energy of the particles or kinetic energy?

Answer 13

Potential energy will always be much smaller than kinetic energy.

Question 14

What is internal energy?

Answer 14

Internal energy is the sum of the randomly distributed kinetic energies and potential energies of the particles in a body.

Question 15

How does the internal energy of a system increase ?

Answer 15

It can either increase by heating the system or having work done on it.

Question 16

During a change of state, what happens to both the potential and kinetic energy of the particle?

Answer 16

The potential energies of the particles change however the kinetic energies do not.

Question 17

What is Avogadro’s Constant?

Answer 17

The number of atoms in exactly 12g of the carbon isotope 12C6. - 6.02X10^23

Question 18

What is a mole?

Answer 18

One mole of any substance has the same number of particles as Avagadro’s constant.

Question 19

How can the total number of molecules N in a sample of a substance be calculated?

Answer 19

N = n x Na where n is the number of moles in the sample

Question 20

What is an ideal gas?

Answer 20

The ideal gas law follows all 5 assumptions perfectly.

The five assumptions follows;
Negligible intermolecular forces except during collisions.
Volume occupied by gas molecules is negligible when compared to the volume of the container
The time of collision is negligible compared to the time between collisions. This implies that collisions are instantaneous.
There are a large number of particles in rapid, random motion
All collisions are perfectly elastic.

Question 21

What is the relationship between pressure and number of particles? (Gas law 0 - Avogadro’s Law)

Answer 21

Pressure is directly proportional to the number of particles, provided the temperature and volume doesn’t change in the container,

Question 22

What is the relationship between volume and pressure? (Gas law 1 - Boyle’s law)

Answer 22

Pressure is inversely proportional to the volume of a gas, provided the mass and temperature of the gas stays constant.

Question 23

What is the relationship between pressure and temperature? (Gas law 2 - Gay Lussac’s law)

Answer 23

Pressure is directly proportional to temperature, provided the volume and mass of the gas does not change.

Question 24

What is the relationship between volume and temperature? (Gas law 3 - Chavel’s law)

Answer 24

Volume is proportional to temperature, provided the pressure and mass of the gas does not change.

Question 25

How do you convert from degrees celsius to kelvin?

Answer 25

Need to +273.15 to a temperature in degrees to get a temperature in Kelvin

Question 26

What is Brownian motion?

Answer 26

The random motion of small particles suspended in a fluid.

Question 27

What is pressure caused by?

Answer 27

The change in momentum of the molecules that collide with the container walls/ surfaces

Question 28

What is temperature proportional to in the molecular kinetic theory model?

Answer 28

The average kinetic energy of the molecules

Question 29

How can molecular kinetic theory explain Boyle’s law?

Answer 29

The pressure of a gas at constant temperature is increased by reducing its volume because the gas molecules travel a smaller distance between collisions with the container walls, so there are more collisions per second and a greater pressure.

Question 30

How can molecular kinetic theory explain the pressure law?

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Answer 30

The pressure of a gas at a constant volume is increased by raising its temperature because this raises the average kinetic energy of the molecules, so their collisions with the container wall are harder and more frequent, resulting in a greater force per unit area on the container walls.

Question 31

How can molecular kinetic theory explain Charle’s law?

Answer 31

The volume of a gas at constant pressure is increased by raising its temperature because this raises the average kinetic energy of the molecules so the particles will spread out more and collide more frequently and harder with the container walls.