Melting
Solid to liquid; melting point of ice.
Melting
Melting
What you'll learn
- Melting — solid changes to liquid when heated to its melting point.
- Ice melts at 0 °C (at normal atmospheric pressure) — key reference for water.
- Melting needs heat energy without temperature rise at the melting point (plateau concept intro).
- NCERT Looking Around 5, Chapter 7 (Experiments with Water) — ice in sun, salt on ice.
Key concepts
Level 1 — Solid to liquid
Verbal: When ice is warmed, it becomes liquid water at 0 °C; more heating then warms the water above 0 °C.
Symbolic: Solid --(heat)--> Liquid at melting point.
| Substance | Melting point (intro) | Observation |
|---|---|---|
| Ice (water) | 0 °C | Puddle forms |
| Butter | ~30–35 °C (approx.) | Softens on hot tawa |
| Wax candle | Low (approx.) | Drips when lit |
NCERT link: Ch 7 — ice cubes in different places melt at different rates.
Level 2 — Energy and everyday melting
Verbal: Heat breaks particle arrangement in solid — particles move more freely as liquid.
Real-life: Kulfi melts on hot day; road tar softens in summer; chocolate melts in pocket.
| Factor | Effect on melting speed |
|---|---|
| Higher temperature | Faster melting |
| Smaller pieces | Faster (more surface area) |
| Salt on ice | Lowers freezing point — ice melts below 0 °C (road de-icing) |
Worked example
Ice cube at 0 °C in a warm room. Describe change.
Step 1 — Heat enters ice at 0 °C.
Step 2 — Ice melts to water at 0 °C.
Step 3 — Water then warms above 0 °C.
Answer: Solid → liquid, then temperature rises.
Why does butter melt on a hot pan before water boils?
Step 1 — Butter melting point much lower than 100 °C.
Step 2 — Pan > butter melting point → liquid butter.
Answer: Different substances have different melting points.
Common mistakes
| Mistake | Why it happens | Fix |
|---|---|---|
| Melting and boiling same | Both need heat | Melting = solid→liquid; boiling = liquid→gas |
| Ice melts instantly at any temp | Ignoring 0 °C for water | Ice at room temp melts because room > 0 °C |
| Cold creates melting | Reversing concepts | Heat causes melting |
| Melt = disappear | Evaporation next step | Liquid water still present — not vanished |
Quick check
- What change is melting?
- At what temperature does ice melt (°C)?
- Name one solid that melts in your kitchen.
- Stretch: Two equal ice cubes — one crushed, one whole — which melts faster? Why?
Revision tip: Time how long an ice cube takes to melt in shade vs sun — record in a table (Ch 7 style experiment).
Open the Practice tab for graded questions on Melting.
Key Takeaways (TL;DR)
- What you'll learn
- Key concepts
- Worked example
- Common mistakes
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