Thermal Physics

Question 1

What is internal energy?

Answer 1

The total kinetic and potential energy of the particles in a system.

Question 2

What does kinetic energy in internal energy depend on?

Answer 2

The speed of particles (temperature-dependent).

Question 3

What does potential energy in internal energy depend on?

Answer 3

Intermolecular forces and separation between particles.

Question 4

How does temperature affect internal energy?

Answer 4

Higher temperature → higher kinetic energy → higher internal energy.

Question 5

Which phase of matter has the highest internal energy?

Answer 5

Gases.

Question 6

Name two ways internal energy can increase.

Answer 6

1. Heating (thermal energy added)
2. Doing work on the system (e.g., compression)

Question 7

Name two ways internal energy can decrease.

Answer 7

1. System loses thermal energy
2. System does work on surroundings (e.g., expansion)

Question 8

What is the First Law of Thermodynamics?

Answer 8

Energy cannot be created or destroyed; internal energy increases by heating or doing work on a system.

Question 9

Formula for the First Law of Thermodynamics?

Answer 9

ΔU=Q+W

Question 10

What happens to internal energy when a gas is compressed?

Answer 10

Work is done on the gas → internal energy increases.

Question 11

What happens to internal energy when a gas expands?

Answer 11

Work is done by the gas → internal energy decreases.

Question 12

What is specific heat capacity?

Answer 12

Energy required to raise the temperature of 1 kg of a substance by 1°C or 1 K.

Question 13

Formula for specific heat capacity?

Answer 13

Q=mcΔθ

Question 14

Does a substance with high specific heat capacity heat up quickly or slowly?

Answer 14

Slowly.

Question 15

Why do good conductors like copper have low specific heat capacities?

Answer 15

They require less energy to increase temperature, allowing faster heat conduction.

Question 16

What is latent heat?

Answer 16

Energy required to change the state of 1 kg of a substance with no temperature change.

Question 17

Formula for latent heat?

Answer 17

Q=mL

Question 18

What is specific latent heat of fusion?

Answer 18

Energy to change 1 kg from solid to liquid (or vice versa) at constant temperature.

Question 19

What is specific latent heat of vaporisation?

Answer 19

Energy to change 1 kg from liquid to gas (or vice versa) at constant temperature.

Question 20

Why is the latent heat of vaporisation of water greater than its latent heat of fusion?

Answer 20

It requires more energy to completely overcome intermolecular forces and do work against atmospheric pressure.

Question 21

What is thermal equilibrium?

Answer 21

When two substances reach the same final temperature after exchanging heat.

Question 22

Energy balance formula for thermal equilibrium?

Answer 22

ΔQ colder=−ΔQ warmer
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Question 23

What is absolute zero in Kelvin and Celsius?

Answer 23

0 K or -273

Question 24

Can the temperature go below 0 K?

Answer 24

No, 0 K is the lowest possible temperature.

Question 25

What happens to the kinetic energy of molecules at absolute zero?

Answer 25

It becomes zero — molecules stop moving.

Question 26

What are the three ideal gas laws?

Answer 26

Boyle’s Law, Charles’s Law, and the Pressure Law.

Question 27

What does Boyle’s Law state?

Answer 27

P∝ 1/V ​(at constant T)

Question 28

Boyle’s Law equation?

Answer 28

P1V1=P2V2 ​

Question 29

What does Charles’s Law state?

Answer 29

V∝T (at constant P)

Question 30

Charles’s Law equation?

Answer 30

V1/T1 = V2/T2 ​

Question 31

What does the Pressure Law state?

Answer 31

P∝T (at constant V)

Question 32

Pressure Law equation?

Answer 32

P1/T1 = P2/T2

Question 33

What is the ideal gas equation?

Answer 33

pV=nRT

Question 34

What assumptions are made about ideal gases?

Answer 34

No intermolecular forces, elastic collisions, negligible molecular volume, and obeys all gas laws.

Question 35

What is the equation for work done by a gas?

Answer 35

W=pΔV

Question 36

When is work done by the gas?

Answer 36

When the gas expands.

Question 37

When is work done on the gas?

Answer 37

When the gas is compressed.

Question 38

How do you calculate moles from mass?

Answer 38

moles= mass (g)/molar mass (g/mol) ​

Question 39

What does the Boyle’s Law practical investigate?

Answer 39

Relationship between pressure and volume at constant temperature

Question 40

Key formula used in analysis?

Answer 40

pV=constant

Question 41

What does the Charles’s Law practical investigate?

Answer 41

Relationship between volume and temperature at constant pressure.

Question 42

What graph is used to confirm Charles’s Law?

Answer 42

Height of gas (∝ volume) vs. temperature in °C.

Question 43

How is absolute zero estimated from the graph?

Answer 43

Extrapolate to where volume = 0 → gives value near -273 °C.