Physical and Chemical Changes - 7.1 When Substances Change [ARCHIVE] Flashcards

1
Q

What is the key feature of a physical change?

A

No new substance is produced during the change.

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2
Q

What are the characteristics of physical changes?

A
  • Change in shape or form
  • Expansion and contraction
  • Change of state
  • Mixing substances
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3
Q

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

A

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

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4
Q

Can physical changes be easily reversed?

A

Yes.

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5
Q

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

A

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

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6
Q

Can changes in shape or form be reversed?

A

Yes, these changes can often be reversed relatively easily.

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7
Q

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

A

They expand and take up more space.

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8
Q

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

A

The volume increases, and the density decreases.

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9
Q

What happens to a substance when it is cooled?

A

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

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10
Q

What is the reverse of expansion?

A

Contraction.

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11
Q

How do thermometers use expansion and contraction to measure temperature?

A

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

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12
Q

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

A

Ethanol and mercury.

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13
Q

What happens when enough heat is applied to a substance?

A

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

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14
Q

What happens to a substance when it is cooled enough?

A

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

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15
Q

What is sublimation and deposition?

A

Sublimation - a solid changes directly to a gas
Deposition - a gas changes directly to a solid.

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16
Q

What happens when a solid is heated enough?

A

It melts and changes into a liquid.

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17
Q

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

A

The heat from your mouth melts it into liquid water.

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18
Q

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

A

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

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19
Q

Why is melting considered a physical change?

A

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

20
Q

What is freezing?

A

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

21
Q

What happens when liquid water is put in the freezer?

A

It forms ice cubes through the process of freezing.

22
Q

What is evaporation?

A

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

23
Q

How does temperature affect evaporation?

A

Evaporation occurs faster as the temperature of the liquid increases.

24
Q

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

A

Because evaporation speeds up as the temperature increases.

25
Q

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

A

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

26
Q

What is condensation?

A

Condensation is when a gas cools and becomes a liquid.

27
Q

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

A

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

28
Q

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

A

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

29
Q

What is mixing?

A

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

30
Q

What does a bucket of different-colored balls represent?

A

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

31
Q

Is mixing considered a chemical or physical change?

A

Mixing is a physical change.

32
Q

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

A

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

33
Q

Why does the solute seem to disappear in a solution?

A

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

34
Q

What is crystallization?

A

Where solute particles rejoin to form crystals when the solvent is removed by boiling or evaporation.

35
Q

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

A

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

36
Q

Is dissolving a physical or chemical change?

A

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

37
Q

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

A

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

38
Q

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

A

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

39
Q

How can gas indicate a chemical change?

A

By smelling the gas or seeing bubbles.

40
Q

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

A

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

41
Q

How do light or temperature changes indicate a chemical change?

A

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

42
Q

What does a permanent color change indicate?

A

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

43
Q

Is mixing paint a chemical or physical change?

A

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

44
Q

What are exothermic reactions?

A

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

45
Q

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

A

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