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.
