3. Particles

Question 1

What is the definition of density?

Answer 1

The mass per unit volume of a material.

Question 2

State the relevant equation for density with units.

Answer 2

⍴ = m/v. Density (kg/m³), Mass (kg), Volume (m³)

Question 3

State the different states of matter in order (least to most) of density of atoms.

Answer 3

Least dense: Gas
Most dense: Solid

Question 4

Describe the particle arrangement of a solid.

Answer 4

Tightly packed in a regular arrangement. Particles can only vibrate on the spot.

Question 5

Describe the particle arrangement of a liquid.

Answer 5

Close together, but with an irregular arrangement. They can flow over each other.

Question 6

Describe the particle arrangement of a gas.

Answer 6

Separated

Question 7

What is always conserved when a substance undergoes a change of state?

Answer 7

Mass.

Question 8

How does a change of state differ from a chemical change?

Answer 8

In a change of state, the material can return to having its previous properties if the change is reversed.

Question 9

What is sublimation?

Answer 9

When a solid changes into a gas without passing through a liquid state.

Question 10

What is evaporation?

Answer 10

When a liquid changes into a gas state.

Question 11

What is the opposite of evaporation?

Answer 11

Condensation

Question 12

When water boils in an open pan why does the mass of the pan of water appear to decrease?

Answer 12

Water has evaporated from the pan and entered the atmosphere as water vapour.

Question 13

Explain the processes involved when a bathroom mirror mists up.

Answer 13

1. Hot water evaporates to form water vapour. 2. The water vapour lands on the cooler mirror. 3. The vapour condenses and returns to liquid state on the mirror’s surface.

Question 14

What is the internal energy of a substance?

Answer 14

The energy stored by the particles. It is the sum of the total kinetic and potential energies that make up the substance.

Question 15

How does heating affect the energy of a substance?

Answer 15

Heating transfers energy to the substance, increasing the energy of the particles.

Question 16

What two things can heating a substance do?

Answer 16

1. Raise its temperature 2. Change the state of the substance.

Question 17

What three factors determine the temperature change of a system?

Answer 17

1. Mass of substance being heated 2. Type of material (Specific heat capacity) 3. Energy inputted into the system.

Question 18

State the equation used to calculate the temperature change when a substance is heated.

Answer 18

ΔE = m c Δ𝛉. Energy (J)

Question 19

Define specific heat capacity.

Answer 19

The amount of energy needed to increase the temperature of 1kg of a substance by 1°C.

Question 20

Describe how the internal energy and temperature of a substance change when a change of state occurs.

Answer 20

The internal energy of the substance will be increased or decreased, but the temperature of the substance will remain constant.

Question 21

Define specific latent heat.

Answer 21

The amount of energy needed to change the state of 1kg of a substance with no change in temperature.

Question 22

State the equation for the energy required to change state.

Answer 22

Energy to change state = mass × specific latent heat. Energy (J)

Question 23

What is the specific latent heat of fusion?

Answer 23

The energy required to change 1kg of a substance from solid state to liquid state without a change in temperature.

Question 24

What is the specific latent heat of vaporisation?

Answer 24

The energy required to change 1kg of a substance from liquid state to gas state (vapour) without a change in temperature.

Question 25

Describe the motion of molecules in a gas.

Answer 25

They are in constant random motion.

Question 26

What factor affects the average kinetic energy of gas molecules?

Answer 26

The temperature of the substance. The higher the temperature, the higher the average kinetic energy of the molecules.

Question 27

What effect does increasing temperature have on the pressure of a gas when held at constant volume?

Answer 27

Pressure of the gas will increase as the temperature increases.

Question 28

Why does pressure increase as temperature increases (at a constant volume)?

Answer 28

1. Kinetic energy of molecules increases. 2. Collisions between molecules become more frequent. 3. Greater rate of change of momentum. 4. Greater force exerted on container walls.

Question 29

Describe the force that the pressure of a gas exerts on the walls of its container.

Answer 29

The net force acts at right-angles to the container’s surface. The force increases as pressure increases.

Question 30

Explain how increasing the volume of a gas results in a decrease of pressure.

Answer 30

1. Molecules become more spread out, so time between collisions increases. 2. This reduces the rate of collisions. 3. Rate of change of momentum decreases, and so force exerted on container decreases, resulting in lower pressure.

Question 31

What is the unit used for pressure?

Answer 31

Pascal (Pa).

Question 32

What increases when you do work on a gas?

Answer 32

The internal energy of the gas, which can also lead to an increase in temperature.

Question 33

Why does the temperature of air inside a bike pump increase when it is pumped?

Answer 33

1. Work is done on a gas when it is compressed. 2. Doing work on a gas increases its internal energy, so it also increases the average kinetic energy of the molecules. 3. Temperature increases with an increase of average kinetic energy.