Physical and Chemical Changes - 7.1 When Substances Change [ARCHIVE] Flashcards
What is the key feature of a physical change?
No new substance is produced during the change.
What are the characteristics of physical changes?
- Change in shape or form
- Expansion and contraction
- Change of state
- Mixing substances
What happens to the substance before and after a physical change?
The substance remains exactly the same before and after the change.
Can physical changes be easily reversed?
Yes.
What happens during a physical change that alters the shape or form of a substance?
A force is applied to break, bend, stretch, crush, twist, or compress the object.
Can changes in shape or form be reversed?
Yes, these changes can often be reversed relatively easily.
What happens to solids, liquids, and gases when they are heated?
They expand and take up more space.
What changes occur in an object’s volume and density during expansion?
The volume increases, and the density decreases.
What happens to a substance when it is cooled?
It contracts, the volume decreases, and the density increases.
What is the reverse of expansion?
Contraction.
How do thermometers use expansion and contraction to measure temperature?
The liquid inside expands and moves up when heated and contracts and moves down when cooled.
What liquids are commonly used in thermometers for expansion and contraction?
Ethanol and mercury.
What happens when enough heat is applied to a substance?
It expands and changes state from solid to liquid (melting) or liquid to gas (evaporation).
What happens to a substance when it is cooled enough?
It contracts and changes state from gas to liquid (condensation) or liquid to solid (freezing/solidification).
What is sublimation and deposition?
Sublimation - a solid changes directly to a gas
Deposition - a gas changes directly to a solid.
What happens when a solid is heated enough?
It melts and changes into a liquid.
What happens when you place an ice cube in your mouth?
The heat from your mouth melts it into liquid water.
Are the solid and liquid states of a substance different after melting?
Yes, their physical properties may be different, but they are made of the same substance.
Why is melting considered a physical change?
Because no new substance is formed; it is the same substance in a different state.
What is freezing?
Freezing is the reverse of melting, where a liquid cools and becomes a solid.
What happens when liquid water is put in the freezer?
It forms ice cubes through the process of freezing.
What is evaporation?
Evaporation occurs when a liquid is warmed and becomes a gas.
How does temperature affect evaporation?
Evaporation occurs faster as the temperature of the liquid increases.
Why do puddles of water dry faster on a hot day?
Because evaporation speeds up as the temperature increases.
What happens to a liquid when it is heated above its boiling point?
Bubbles of gas form within the liquid, and the liquid boils.
What is condensation?
Condensation is when a gas cools and becomes a liquid.
Why does moisture form on the outside of a cold can of soft drink?
Water vapor in the air condenses on the cold surface of the can to form liquid water.
Why does ‘fog’ come out of your mouth on a cold day?
The water vapour in your breath condenses into tiny droplets, forming a mist.
What is mixing?
Mixing two substances is a physical change where the substances combine but no new substances are formed.
What does a bucket of different-colored balls represent?
It represents a mixture where the balls mix, but no new balls are formed.
Is mixing considered a chemical or physical change?
Mixing is a physical change.
What happens when a solid (solute) dissolves in a liquid (solvent)?
They form a solution, which is a mixture where the solute spreads evenly throughout the solvent.
Why does the solute seem to disappear in a solution?
The solute is broken into particles so small they become invisible to the naked eye (dissolving).
What is crystallization?
Where solute particles rejoin to form crystals when the solvent is removed by boiling or evaporation.
What happens when sugar is dissolved in water and the water evaporates?
The sugar is left behind as crystals, reversing the dissolving process.
Is dissolving a physical or chemical change?
Dissolving is a physical change because the solute and solvent retain their original properties.
How can you distinguish between a chemical change and a physical change?
If a new substance has been produced, it is a chemical change.
What states can the new substance formed in a chemical change be?
The new substance could be a solid, liquid, or gas.
How can gas indicate a chemical change?
By smelling the gas or seeing bubbles.
What is a precipitate, and how does it indicate a chemical change?
A precipitate is a new solid forming in a clear solution, indicating a chemical change.
How do light or temperature changes indicate a chemical change?
Seeing light or feeling a temperature change suggests a chemical reaction has occurred.
What does a permanent color change indicate?
It usually indicates a chemical change because a new substance with a different color is formed.
Is mixing paint a chemical or physical change?
It is a physical change because no new substance is formed, just a mixture of particles.
What are exothermic reactions?
Chemical reactions that release large amounts of heat and light energy, such as fires and explosions.
What is a precipitate, and how does it indicate a chemical change?
A precipitate is a new solid formed from a solution, like scale in pipes or kidney stones.
