Changes of State and Particle Model

Question 1

What is the definition of density? State the relevant equation with units.

Answer 1

The mass per unit volume of a material
⍴=m/v

Question 2

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

Answer 2

Least dense: Gas
Liquid
Most dense: Solid

Question 3

Describe the particle arrangement of a solid.

Answer 3

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

Question 4

Describe the particle arrangement of a liquid.

Answer 4

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

Question 5

Describe the particle arrangement of a gas.

Answer 5

Separated, with no regular arrangement. Particles can move freely.

Question 6

What is always conserved when a substance changes state?

Answer 6

Mass

Question 7

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

Answer 7

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

Question 8

What is sublimation?

Answer 8

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

Question 9

What is evaporation?

Answer 9

When a liquid changes into a gas state.

Question 10

What is condensation?

Answer 10

When a gas changes into a liquid state.

Question 11

What is the internal energy of a substance?

Answer 11

The energy stored by the particles
The sum of the total kinetic and potential energies that make up the system

Question 12

How does heating affect the energy of a substance?

Answer 12

Heating transfers energy to the substance
It increases the energy of the particles that make up the substance

Question 13

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

Answer 13

ΔE = m c Δ𝛉
Energy (J), Mass (kg), Specific Heat
Capacity (J/kg/°C), Temperature (°C)

Question 14

Define specific heat capacity

Answer 14

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

Question 15

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

Answer 15

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

Question 16

Define specific latent heat.

Answer 16

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

Question 17

State the equation for the energy required to change state.

Answer 17

Energy to change state = mass x specific latent heat

Question 18

What is the specific latent heat of fusion?

Answer 18

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

Question 19

What is the specific latent heat of vaporization?

Answer 19

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

Question 20

What factor affects the average kinetic energy of gas molecules?

Answer 20

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

Question 21

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

Answer 21

The kinetic energy of molecules increases
Collisions between molecules becomes more frequent
Greater rate of change of momentum
Greater force and therefore pressure

Question 22

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

Answer 22

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