3. Changes of State

Question 1

Explain the term: “MELTING”

Answer 1

MELTING is the change of state that occurs when a solid becomes a liquid.

Question 2

Explain the term: “FREEZING”

Answer 2

FREEZING is the change of state that occurs when a liquid becomes a solid.

Question 3

Explain the term: “EVAPORATING”

Answer 3

EVAPORATION is the change of state that occurs when a liquid changes to a gas.

Question 4

Explain the term: “CONDENSING”

Answer 4

CONDENSING is the change of state that occurs when a gas changes to a liquid.

(opposite of evaporation)

Question 5

Explain the term: “SUBLIMATION”

Answer 5

SUBLIMATION is the change of state that occurs when a solid changes to a gas (without becoming a liquid first).

Note, if a solid is heated, it usually becomes a liquid first. With ‘sublimation’, this step is missed out.

Question 6

Can you name 2 examples of substances which can ‘sublime’?

Answer 6

Carbon Dioxide
Iodine

Question 7

Suggest a single word which best describes the following changes:

1. Jelly setting in the fridge
2. Puddles drying up on a hot day
3. Dry ice producing fog at a disco

Answer 7

1. Jelly setting in the fridge - FREEZING
2. Puddles drying up on a hot day - EVAPORATION
3. Dry ice producing fog at a disco - SUBLIMATION

Question 8

Can you describe the processes shown in the following diagram:

Answer 8

Question 9

What is the difference between a ‘PHYSICAL CHANGE’ and a ‘CHEMICAL CHANGE’?

Answer 9

Changes in temperature can cause matter to move from one state to another, but its composition remains the same. This is a PHYSICAL CHANGE.

A CHEMICAL CHANGE would turn the substance into something new.

Question 10

What is the MELTING point?

Answer 10

The melting point is the temperature at which a solid becomes a liquid.

Before this is the freezing point also!!

Question 11

What is the BOILING point?

Answer 11

The boiling point is the temperature at which a liquid becomes a gas.

Question 12

The table below shows the melting and boiling points to four different substances:

a. Which substance has the lowest boiling point?
b. What physical state would D be in at 0°C?
c. Which substances are liquids at 90°C?

Answer 12

Question 13

Describe the conditions under which water will evaporate

Answer 13

Water evaporates between 0°C - 100°C but is fastest at 100°C

Question 14

Explain the process of evaporation in terms of energy required and temperature of the surrounding

Answer 14

When particles acquire sufficient energy from their surroundings, they evaporate. This results in a drop in temperature in the surroundings.

Question 15

Define the term compression

Answer 15

Compression is the process of squeezing particles that are not touching closer together.

Question 16

Use kinetic theory to explain why gases can be compressed

Answer 16

A substance in the gas state can be compressed because there is empty space between the particles.

Question 17

Use kinetic theory to explain why liquids and solids cannot be compressed

Answer 17

A substance in the liquid or solid state cannot be compressed because the particles are already touching

Question 18

Give some examples of useful compression

Answer 18

Question 19

Explain the term diffusion

Answer 19

Diffusion is the movement of particles from an area of higher concentration to an area of lower concentration, driven by the random motion of particles. This process continues until there is an even distribution of particles.

Question 20

Explain how diffusion occurs in GASES

Answer 20

Gas particles spread out from an area where they are concentrated to an area where they are less concentrated. These movements result in gas particles mixing with other gas particles.
.
.

e.g. Imagine you spray some air freshener in one corner of a room. At first, the gas particles in the spray are concentrated near the nozzle. As they move around, they collide with the air particles and spread out into the rest of the room. Eventually, the scent can be smelled everywhere because the gas particles have diffused evenly throughout the room.

Question 21

Explain how diffusion occurs in LIQUIDS

Answer 21

Diffusion in liquids happens when the particles of one liquid spread out and mix with the particles of another liquid or substance, without needing to stir or shake them. This happens because the particles in a liquid are always moving around randomly.
.
.

E.g. Imagine you drop a bit of food colouring into a glass of water:
1. At first, the colouring stays in one spot and looks dark.
2. After a while, the colouring spreads out on its own, without stirring, and mixes with the water.
3. Eventually, the whole glass of water becomes the same light colour because the food colouring has diffused through the liquid.

Question 22

Using kinetic theory, explain why liquids and gases are able to undergo diffusion but solids cannot.

Answer 22

Liquids and gases can undergo diffusion because their particles are free to move. In solids, particles are tightly packed in a fixed arrangement and cannot move freely or diffuse.

Question 23

State what is meant by the term ‘MISCIBLE’

Answer 23

The term “miscible” means that two liquids can mix together completely and evenly, without separating. When two liquids are miscible, they blend into one uniform liquid.
.
.

E.g. Water and Orange Juice: When you mix them, they combine fully.

Question 24

Explain the decrease in volume exhibited by ‘miscible’ liquids

Answer 24

When miscible liquids are combined, the total volume of the mixture can sometimes be less than the sum of their original volumes. This happens because the particles of the two liquids fit together more closely when they mix.