Freezing
Changes of State: Freezing
Freezing
Freezing: Liquid to Solid
What you'll learn
- Define freezing and identify the freezing point.
- Give examples of liquids that freeze on cooling.
- Explain that freezing is the opposite of melting.
- Connect freezing to everyday Indian examples.
Key concepts
Level 1 - Meaning of freezing
Freezing is the change of a liquid into a solid when it is cooled. Water placed in a freezer turns into solid ice; this is freezing.
Level 2 - Freezing point
Water freezes at 0 degrees Celsius at normal sea-level pressure. Below this temperature, liquid water changes into solid ice.
Level 3 - Freezing and melting are opposites
Freezing removes heat from a liquid until it becomes solid, while melting adds heat to a solid until it becomes liquid. Ice that melts into water can be frozen again by cooling it back down.
Level 4 - Indian context
In cold hill regions like Kashmir and Ladakh, lake water can freeze over completely in winter. At home, ice trays filled with water are kept in the freezer to make ice cubes for drinks.
NCERT anchor: Looking Around 4, general observation of cooling and changes in materials (freezing of water into ice)
Worked example
Freezing water into ice cubes
Step 1 - Fill an ice tray with liquid water.
Step 2 - Place the tray inside a freezer.
Step 3 - Leave it for several hours.
Step 4 - Take out the tray and see solid ice cubes.
Answer: Cooling the water in the freezer froze it into solid ice.
Freezing juice into ice lollies
Step 1 - Pour liquid fruit juice into ice-lolly moulds.
Step 2 - Place the moulds in the freezer.
Step 3 - Wait until the juice becomes hard and solid.
Step 4 - Remove the mould to get a solid, frozen ice lolly.
Answer: The liquid juice froze into a solid ice lolly on cooling.
Common mistakes
| Mistake | Why it happens | Fix |
|---|---|---|
| Freezing and cooling down slightly are the same | Both involve lowering the temperature | Freezing means the liquid actually turns solid, not just becomes cooler |
| Frozen ice takes up less space than the water it came from | Ice looks like a smaller solid block | Ice actually takes up slightly more space than the same amount of liquid water |
| Freezing cannot be undone | Ice looks permanently solid | Freezing is reversible; ice can melt back into water when warmed |
| Only water can freeze | Water is the most familiar example | Milk, juice, and other liquids can also freeze into solids when cooled enough |
Quick check
- What is freezing?
- What is the freezing point of water?
- How is freezing the opposite of melting?
- Give one example of freezing used at home.
- Stretch: Explain why ice cubes take up slightly more space than the water used to make them.
Revision tip: Freezing turns a liquid into a solid when it is cooled to its freezing point.
Open the Practice tab for graded questions on Freezing.
Key Takeaways (TL;DR)
- What you'll learn
- Key concepts
- Worked example
- Common mistakes
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