Thermal Properties

Question 1

What are the three states of matter?

Answer 1

Solid, Liquid, Gas

Question 2

How are molecules arranged in solids, liquids, and gases?

Answer 2

• Solids: Regular arrangement, closely packed
• Liquids: Irregular arrangement, close together
• Gases: Irregular arrangement, far apart

Question 3

How does intermolecular distance change across states of matter?

Answer 3

• Solids: Molecules are closely packed
• Liquids: Molecules are close together
• Gases: Molecules are far apart

Question 4

How does intermolecular force compare in different states?

Answer 4

• Solids: Very strong
• Liquids: Strong
• Gases: Very weak

Question 5

Which states of matter are compressible?

Answer 5

Only gases are compressible; solids and liquids are incompressible.

Question 6

How does motion differ between solids, liquids, and gases?

Answer 6

• Solids: Vibrate in fixed positions
• Liquids: Pass by each other
• Gases: Move randomly and freely

Question 7

Why are solids and liquids incompressible while gases are compressible?

Answer 7

• Solids: Molecules are tightly packed with strong forces.
• Liquids: Molecules are close together with strong forces.
• Gases: Molecules are far apart with weak forces, allowing compression.

Question 8

What is Brownian motion?

Answer 8

The random movement of particles suspended in a fluid due to collisions with fast-moving molecules in the fluid.

Question 9

What happens to a dust particle in air?

Answer 9

It moves freely and randomly in a zigzag path and is seen as a speck of light.

Question 10

Why does Brownian motion occur?

Answer 10

Fast-moving air molecules hit the dust particle from all directions, causing random motion.

Question 11

How does expansion compare in solids, liquids, and gases?

Answer 11

Expansion in solids < Expansion in liquids < Expansion in gases.

Question 12

Why do gases expand more than solids?

Answer 12

Gas molecules are far apart with weak forces, allowing more expansion when heated.

Question 13

What happens to a bimetallic strip when heated?

Answer 13

It bends towards the metal with lower expansion.

Question 14

Give two disadvantages of expansion.

Answer 14

• Expansion in train railways
• Expansion in electric cables

Question 15

What is Boyle’s Law?

Answer 15

At constant temperature, pressure is inversely proportional to volume
P₁V₁ = P₂V₂

Question 16

What happens to gas pressure when volume decreases?

Answer 16

Pressure increases because molecules collide more frequently with container walls exerting more force and pressure.

Question 17

What is the relationship between pressure and temperature at constant volume?

Answer 17

Pressure is directly proportional to temperature.

Question 18

What happens to gas molecules when temperature increases?

Answer 18

They gain kinetic energy, move faster, and collide more frequently, exerting more force and pressure.

Question 19

What is the relationship between volume and temperature at constant pressure?

Answer 19

Volume is directly proportional to temperature.

Question 20

How do air molecules exert pressure on container walls?

Answer 20

Randomly and freely moving air molecules collide with the walls of the cylinder and rebound causing a change in momentum, which exerts force and pressure

Question 21

What is the formula for heat energy?

Answer 21

Q = mcΔT
where:
* Q = Energy (Joules)
* m = Mass (kg or g)
* c = Specific heat capacity (J/kg°C | J/g°C)
* ΔT = Temperature change (°C)

Question 22

What is thermal capacity?

Answer 22

The amount of energy needed to raise the temperature of a body by 1°C.

Question 23

What is specific heat capacity?

Answer 23

The amount of energy required to raise the temperature of 1 kg/g of a substance by 1°C.

Question 24

Why do materials with high thermal capacity take longer to heat or cool?

Answer 24

They require more energy to change temperature.

Question 25

What happens to kinetic and potential energy during a temperature change?

Answer 25

* Kinetic energy increases * Potential energy remains constant

Question 26

What happens to kinetic and potential energy during a change in state?

Answer 26

* Kinetic energy remains constant * Potential energy increases (for melting/boiling) or decreases (for condensation/freezing)

Question 27

Why does evaporation cause cooling?

Answer 27

The most energetic surface molecules absorb energy from remaining liquid, leaving the remaining liquid with less energy and temperature

Question 28

How can you increase the rate of evaporation?

Answer 28

* Increase temperature * Increase air flow * Increase surface area * Decrease humidity * Decrease liquid depth

Question 29

How does conduction transfer heat (in metals)?

Answer 29

Thermal energy is transferred through metals by conduction. This is due to collisions between vibrating atoms and free electrons through atoms going from the hot to cold part

Question 30

What materials are good conductors?

Answer 30

Metals (e.g., copper, aluminum) because they have many free electrons.

Question 31

How can conduction be reduced?

Answer 31

Using insulators like plastic, wood, and rubber.

Question 33

Where does convection occur?

Answer 33

In liquids and gases.

Question 34

Why does hot air rise?

Answer 34

It has lower density and is replaced by cooler, denser air.

Question 35

What is a sea breeze?

Answer 35

Cool air from the sea replaces warm air rising from land.

Question 36

What is a land breeze?

Answer 36

Cool air from land replaces warm air rising from the sea.

Question 37

How can heat loss by convection be reduced?

Answer 37

* Using a vacuum * Using insulators * Trapping air between layers * Using a lid

Question 38

How does radiation transfer heat?

Answer 38

Through electromagnetic (infrared) waves, even in a vacuum.

Question 39

What are good absorbers of radiation?

Answer 39

Dark, dull, rough, black surfaces.

Question 40

What are good reflectors of radiation?

Answer 40

Shiny, polished, white, and silver surfaces.

Question 41

What is the greenhouse effect?

Answer 41

Greenhouse gases trap infrared radiation, increasing Earth's temperature.

Question 42

How can Earth's temperature remain stable?

Answer 42

Incoming radiation from space = Outgoing radiation from Earth.

Question 43

How does a car radiator lose heat?

Answer 43

1. Heat transfers from engine to fluid by conduction. 2. Heat transfers from fluid to radiator by conduction. 3. The radiator is black with a large surface area to increase radiation emission.

Question 44

How does a vacuum flask prevent heat loss?

Answer 44

* Double walls with vacuum: Reduces conduction & convection. * Silvered walls: Reduces radiation loss. * Lid: Reduces heat loss by convection.

Question 45

What is the difference between specific heat capacity and thermal capacity?

Answer 45

* Specific heat capacity is the energy required to raise the temperature of 1 kg (or 1 g) of a substance by 1°C, * Thermal capacity is the total energy needed to raise the temperature of an object by 1°C (specific heat capacity multiplied by its mass).

Question 46

What are the three primary modes of heat transfer, and what is a key characteristic of each?

Answer 46

* Conduction: Energy transfer via direct collisions between particles (depends on thermal conductivity). * Convection: Energy transfer through the bulk movement of fluids (driven by density differences). * Radiation: Energy transfer via electromagnetic waves (does not require a medium).

Question 47

How do pressure, volume, and temperature relate in an ideal gas (for constant T, V, or P)?

Answer 47

* At constant temperature (Boyle’s Law): 𝑃 ∝ 1/𝑉 * At constant volume: 𝑃 ∝ 𝑇 * At constant pressure: 𝑉 ∝ 𝑇

Question 48

Why does the temperature remain constant during a phase change even though energy is transferred?

Answer 48

During a phase change, the energy is used to break or form intermolecular bonds rather than increasing the kinetic energy of the particles, so the temperature remains constant until the phase change is complete.