Thermal Physics

Question 1

Define absolute zero

Answer 1

The lowest possible temperature a substance can have, where there is no particle movement. -273°C or 0K

Question 2

State the conversion equation from degrees Celsius to kelvins

Answer 2

K = C + 273

Question 3

What happens to a particle’s average speed, average kinetic energy and distribution curve as temperature increases?

Answer 3

• As temperature increases, average particle speed increases
• As temperature increases, average particle kinetic energy increases
• The distribution curve is more spread out

Question 4

Why is average speed and kinetic energy used for particles in a gas?

Answer 4

As the particles in a gas don’t all travel at the same speed

Question 5

What is internal energy?

Answer 5

The sum of kinetic and potential energies of all a body’s randomly distributed particles

Question 6

When do gases not have potential energy?

Answer 6

When the gas is an ideal gas

Question 7

How can the internal energy of a system be increases?

Answer 7

• By heating the system
• By doing work to transfer energy to the sytem, i.e changing shape

Question 8

In what direction is heat transfer?

Answer 8

• From hotter substances to colder substances
• The higher the difference in temperature between the substances, the faster the heat transfer

Question 9

Define specific heat capacity

Answer 9

The amount of energy needed to raise the temperature of 1kg of the substance by 1K

Question 10

When a substance changes state, what happens to its internal energy, kinetic energy, and temperature?

Answer 10

• Internal energy changes as potential energy of particles is altered
• Kinetic energy stays the same
• Temperature stays the same

Question 11

Describe the graph of temperature against internal energy for a sample of water

Answer 11

• Constant gradient until 100°C as particles gain kinetic energy as water is heated
• Horizontal line as kinetic energy stays same while potential energy increases to break bonds
• Constant gradient past 100°C once water becomes vapour

Question 12

Define specific latent heat

Answer 12

The amount of energy needed to change the state of 1kg of a substance

Question 13

State Boyle’s Law

Answer 13

• At a constant temperature the pressure and volume of a gas are inversely proportional
• pV = constant

Question 14

What is an ideal gas?

Answer 14

A gas which obeys boyle’s law at all temperatures

Question 15

States Charles’ Law

Answer 15

• At constant pressure, the volume of a gas is directly proportional to its absolute temperature
• V/T = constant

Question 16

Describe the graph of volume against temperature for an ideal gas at constant pressure on the degrees Celsius scale

Answer 16

• x axis = absolute zero = -273°C
• constant gradient

Question 17

Describe the graph of volume against temperature for an ideal gas at a constant pressure on the kelvin scale

Answer 17

• x axis = absolute zero = 0K
• constant gradient

Question 18

State the pressure law

Answer 18

• At constant volume, the pressure of an ideal gas is directly proportional to its absolute temperature
• P/T = constant

Question 19

Define the Avogadro constant

Answer 19

The number of atoms in exactly 12g of carbon isotope

Question 20

State the equation for the number of molecules

Answer 20

N = n(mol) x NA

Question 21

State the equation the combination of the three gas laws give

Answer 21

PV/T = constant

Question 22

State the ideal gas equation for n moles

Answer 22

pV = nRT

Question 23

State the ideal gas equation for N molecules

Answer 23

pV = NkT

Question 24

What is the conversion from litres to volume

Answer 24

1000 litres = 1m³

Question 25

State the equation for work done for a gas to expand or contract at a constant temperature

Answer 25

Work done = p∆V

Question 26

What does the area under a pressure-volume graph represent

Answer 26

The work done

Question 27

What are the assumptions in kinetic theory?

Answer 27

- All molecules of the gas are identical - The gas contains a large number of molecules - Compared to the container, the molecules' volume is negligible - The molecules continuously move about randomly - The motion of molecules follow newton's laws - Collisions between molecules themselves or walls of the container are elastic - Between collisions, molecules move in a straight line - Forces that act during collisions last for much less time than forces during collisions

Question 28

What are empirical laws, giving an example?

Answer 28

Laws which are based of observation and evidence, i.e the gas laws

Question 29

What are theories?

Answer 29

Predictions based on assumptions and derivations from knowledge and already developed theories, i.e Kinetic theory

Question 30

Define Brownian motion

Answer 30

The motion of a visible particle suspended in a fluid being randomly affected by particles invisible to the human eye

Question 31

What are the units for specific heat capacity?

Answer 31

J/KgK

Question 32

When water turns to steam, what happens to its volume?

Answer 32

Volume increases 1000x as it expands

Question 33

What is the specific heat capacity of water?

Answer 33

4200 J/KgK

Question 34

State 6 assumptions of Brownian motion

Answer 34

- Collision between molecules themselves or between the molecules and walls of the container are perfectly elastic - The time during a collision is negligible compared to the time between collisions - The molecules continually move about randomly - The molecules move in a straight line between collisions - The molecules have a negligible volume compared to the volume of the container - All molecules of the gas are identical

Question 35

Define thermal equilibrium

Answer 35

No net transfer of thermal energy between objects

Question 36

What is the potential energies of each state of matter?

Answer 36

- Solid = Low - Liquid = Max - Gas = 0, no bonds

Question 37

What are the equations for number of moles?

Answer 37

- n = mass(g)/atomic mass - n = mass(g)/molar mass

Question 38

What is the equation for mass(kg) of atoms in a container involving molar mass(kg/mol)?

Answer 38

Mass(kg) = molar mass/NA where NA is Avogadro's constant