Phase Changes and Heating Curves
Temperature plateaus during melting and boiling.
About this topic
Phase changes are transitions between solid, liquid and gas: melting, freezing, vaporisation, condensation, sublimation and deposition. A heating curve plots temperature against energy added; sloped sections show heating of one phase, and flat plateaus show a phase change, when energy breaks intermolecular attractions without raising temperature.
The energy for each plateau is called latent heat. For melting, q = m × ΔHfus, and for boiling q = m × ΔHvap. For water, ΔHfus is 334 J/g and ΔHvap is 2260 J/g, so boiling takes about seven times more energy than melting because particles must be completely separated. Along the sloped parts, q = m × c × ΔT, where c is the specific heat capacity (4.18 J/g·°C for liquid water, about 2.1 for ice and steam).
Worked example: heating 10 g of ice at minus 10 degrees Celsius to steam at 110 involves five steps: warming ice, melting, warming water, boiling and warming steam, with a total of roughly 30 kJ, dominated by vaporisation. This is why steam burns are worse than boiling water burns, and why sweating cools you. Refrigerators and air conditioners use evaporation and condensation to move heat.
A misconception is that temperature rises while a substance melts; it stays constant until all is melted. Also, the cooling curve is simply the reverse.
Key ideas
- Energy breaks intermolecular forces
- Latent heat of fusion and vaporization
- Slopes show specific heat
Quick check
Use cases: where Phase Changes and Heating Curves helps
- Homework: review the key idea behind Phase Changes and Heating Curves before you start a problem set.
- Exam revision: use the quick check to test whether you can recall Phase Changes and Heating Curves without notes.
- Visual learning: play with the interactive lab to see how Phase Changes and Heating Curves changes when you adjust its inputs.
- Teaching a friend: explain Phase Changes and Heating Curves in your own words, then compare your version with the key ideas.
Chemistry explains medicine, food, cleaning products, fuels and building materials.
Frequently asked questions
What is Phase Changes and Heating Curves?
Temperature plateaus during melting and boiling.
What will I learn in Phase Changes and Heating Curves?
Energy breaks intermolecular forces. Latent heat of fusion and vaporization. Slopes show specific heat.
Is Phase Changes and Heating Curves part of Chemistry?
Yes. It is one of 150 Chemistry topics on LearnViz HighSchoolEdu, with 3 key ideas, a live animation and a quick check.
Does the Phase Changes and Heating Curves lab work on a phone or tablet?
Yes. The animation resizes to fit your screen and supports touch, so you can drag, tap and slide with your finger.
How should I study Phase Changes and Heating Curves?
Read the summary and key ideas first, play with the interactive lab to see the idea in motion, then answer the quick check. If you get a question wrong, go back to the key idea it tests.
Do I need an account, and is my progress saved?
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