Physical and Chemical Changes - 7.1 When Substances Change

Question 1

What is the key feature of a physical change?

Answer 1

No new substance is produced during the change.

Question 2

What are examples of physical changes?

Answer 2

Change in shape or form, expansion and contraction, change of state, or mixing substances.

Question 3

What happens to the substance before and after a physical change?

Answer 3

The substance remains exactly the same before and after the change.

Question 4

Can physical changes be easily reversed?

Answer 4

Yes.

Question 5

What happens during a physical change that alters the shape or form of a substance?

Answer 5

A force is applied to break, bend, stretch, crush, twist, or compress the object.

Question 6

Can changes in shape or form be reversed?

Answer 6

Yes, these changes can often be reversed relatively easily.

Question 7

What happens to solids, liquids, and gases when they are heated?

Answer 7

They expand and take up more space.

Question 8

What changes occur in an object’s volume and density during expansion?

Answer 8

The volume increases, and the density decreases.

Question 9

What happens to a substance when it is cooled?

Answer 9

It contracts, the volume decreases, and the density increases.

Question 10

What is the reverse of expansion?

Answer 10

Contraction.

Question 11

How do thermometers use expansion and contraction to measure temperature?

Answer 11

The liquid inside expands and moves up when heated and contracts and moves down when cooled.

Question 12

What liquids are commonly used in thermometers for expansion and contraction?

Answer 12

Ethanol and mercury.

Question 13

What happens when enough heat is applied to a substance?

Answer 13

It expands and changes state from solid to liquid (melting) or liquid to gas (evaporation).

Question 14

What happens to a substance when it is cooled enough?

Answer 14

It contracts and changes state from gas to liquid (condensation) or liquid to solid (freezing/solidification).

Question 15

What is sublimation and deposition?

Answer 15

Sublimation is when a solid changes directly to a gas, and deposition is when a gas changes directly to a solid.

Question 16

What happens when a solid is heated enough?

Answer 16

It melts and changes into a liquid.

Question 17

What happens when you place an ice cube in your mouth?

Answer 17

The heat from your mouth melts it into liquid water.

Question 18

Are the solid and liquid states of a substance different after melting?

Answer 18

Yes, their physical properties may be different, but they are made of the same substance.

Question 19

Why is melting considered a physical change?

Answer 19

Because no new substance is formed; it is the same substance in a different state.

Question 20

What is freezing?

Answer 20

Freezing is the reverse of melting, where a liquid cools and becomes a solid.

Question 21

What happens when liquid water is put in the freezer?

Answer 21

It forms ice cubes through the process of freezing.

Question 22

What is evaporation?

Answer 22

Evaporation occurs when a liquid is warmed and becomes a gas.

Question 23

How does temperature affect evaporation?

Answer 23

Evaporation occurs faster as the temperature of the liquid increases.

Question 24

Why do puddles of water dry faster on a hot day?

Answer 24

Because evaporation speeds up as the temperature increases.

Question 25

What happens to a liquid when it is heated above its boiling point?

Answer 25

Bubbles of gas form within the liquid, and the liquid boils.

Question 26

What is condensation?

Answer 26

Condensation is when a gas cools and becomes a liquid.

Question 27

Why does moisture form on the outside of a cold can of soft drink?

Answer 27

Water vapor in the air condenses on the cold surface of the can to form liquid water.

Question 28

Why does ‘fog’ come out of your mouth on a cold day?

Answer 28

The water vapour in your breath condenses into tiny droplets, forming a mist.

Question 29

What is mixing?

Answer 29

Mixing two substances is a physical change where the substances combine but no new substances are formed.

Question 30

What does a bucket of different-colored balls represent?

Answer 30

It represents a mixture where the balls mix, but no new balls are formed.

Question 31

Is mixing considered a chemical or physical change?

Answer 31

Mixing is a physical change.

Question 32

What happens when a solid (solute) dissolves in a liquid (solvent)?

Answer 32

They form a solution, which is a mixture where the solute spreads evenly throughout the solvent.

Question 33

What is an example of dissolving in liquids?

Answer 33

Liquid food coloring dissolving in water.

Question 34

Why does the solute seem to disappear in a solution?

Answer 34

The solute is broken into particles so small they become invisible to the naked eye.

Question 35

What is crystallization?

Answer 35

It’s the process where solute particles rejoin to form crystals when the solvent is removed by boiling or evaporation.

Question 36

What happens when sugar is dissolved in water and the water evaporates?

Answer 36

The sugar is left behind as crystals, reversing the dissolving process.

Question 37

Is dissolving a physical or chemical change?

Answer 37

Dissolving is a physical change because the solute and solvent retain their original properties.

Question 38

How can you distinguish between a chemical change and a physical change?

Answer 38

If a new substance has been produced, it is a chemical change.

Question 39

What states can the new substance formed in a chemical change be?

Answer 39

The new substance could be a solid, liquid, or gas.

Question 40

How can gas indicate a chemical change?

Answer 40

By smelling the gas or seeing bubbles.

Question 41

What is a precipitate, and how does it indicate a chemical change?

Answer 41

A precipitate is a new solid forming in a clear solution, indicating a chemical change.

Question 42

How do light or temperature changes indicate a chemical change?

Answer 42

Seeing light or feeling a temperature change suggests a chemical reaction has occurred.

Question 43

What does a permanent color change indicate?

Answer 43

It usually indicates a chemical change because a new substance with a different color is formed.

Question 44

What happens when paper, wood, or a match is burned?

Answer 44

They turn into black powder (carbon), showing a chemical change.

Question 45

Is mixing paint a chemical or physical change?

Answer 45

It is a physical change because no new substance is formed, just a mixture of particles.

Question 46

What are exothermic reactions?

Answer 46

Chemical reactions that release large amounts of heat and light energy, such as fires and explosions.

Question 47

What is a precipitate, and how does it indicate a chemical change?

Answer 47

A precipitate is a new solid formed from a solution, like scale in pipes or kidney stones.