What Are Melting, Boiling, and Sublimation?
Melting, boiling, and sublimation are three solid-to-liquid/gas phase changes. Each has a characteristic temperature where it occurs, and each requires energy input (heat) to break particle bonds.
Melting is solid → liquid at melting point. Boiling is liquid → gas at boiling point. Sublimation is solid → gas without melting. All three are endothermic and occur at fixed temperatures for each substance.
- •Happens at melting point (0°C for ice)
- •Particles vibrate more, break bonds
- •Absorbs energy (latent heat of fusion)
- •Reversible (refreezing)
- •Happens at boiling point (100°C for water)
- •Bubbles form throughout liquid
- •Absorbs more energy (latent heat of vaporization)
- •Reversible (condensation)
Step-by-step worked examples
Ice melts at 0°C. How much energy is released when 1 kg refreezes?
Melting is solid → liquid (absorbs heat). Refreezing is liquid → solid (releases heat). Latent heat of fusion for ice ≈ 334 kJ/kg. Energy released = 1 kg × 334 kJ/kg = 334 kJ
Water boils at 100°C at sea level. Is it possible to boil water at 50°C?
At lower atmospheric pressure, water boils at lower temperatures. In a vacuum or high altitude, water boils below 100°C. So yes, it's possible if pressure decreases.
Dry ice (solid CO₂) sublimes. Why doesn't it melt first?
CO₂'s triple point is at −56.6°C and 5.1 atm. At normal pressure (1 atm), solid CO₂ cannot be liquid. So it bypasses the liquid stage and sublimates directly to gas.
Flashcards
Quick quiz
Q1.When does sublimation occur?
Q2.Which requires more energy: melting ice or boiling water?
Q3.Can water boil at 50°C?
Q4.What is an example of sublimation?
The full card deck, worked steps and AI-tutor support for “What Are Melting, Boiling, and Sublimation?” are in Notek — study by hand before your exam.
Common mistakes
Thinking melting and boiling happen at the same temperature for all substances. — Correct: Each substance has its own characteristic melting and boiling points.
Assuming sublimation only occurs with rare materials like dry ice. — Correct: Sublimation is common — ice can sublime in dry conditions, and naphthalene sublimates at room temperature.
Confusing the latent heat of fusion with latent heat of vaporization. — Correct: Fusion (melting) requires less energy; vaporization (boiling) requires much more.
Forgetting that boiling point depends on pressure. — Correct: Higher pressure → higher boiling point; lower pressure → lower boiling point.
FAQ
What is the latent heat of fusion?
The energy absorbed by a solid to melt into a liquid at constant temperature. For water: ~334 kJ/kg.
What is the latent heat of vaporization?
The energy absorbed by a liquid to boil into a gas at constant temperature. For water: ~2256 kJ/kg.
Why does water boil at different temperatures at high altitude?
Lower atmospheric pressure means lower boiling point. At high altitude, water boils below 100°C.
Is sublimation the opposite of deposition?
Yes — sublimation is solid → gas; deposition is gas → solid (the reverse).