Teacher sheet · Ages 15–16 · about 45–50 minutes
States of matter: kinetic theory and latent heat
Lesson page: echoesof.science/school/states-of-matter/ages-15-16/ · Pupil worksheet: echoesof.science/school/states-of-matter/ages-15-16/print/
Learning aims
- Explain the states of matter with particles, forces and kinetic energy.
- Use the kinetic-molecular theory and the link between temperature and kinetic energy.
- Name all six phase transitions and explain the constant temperature during a change of state.
- Calculate latent heat energies; interpret a heating curve.
Lesson plan
| Time | Activity |
|---|---|
| 5 min | Starter: why do you feel cold when you get out of a swimming pool? |
| 10 min | Read the text; work through the latent heat conversion. |
| 25 min | Heating-curve practical in pairs (readings every 30 s). |
| 5 min | Plot the graph and discuss the plateau. |
| 5 min | Quiz, or Phase change detective as homework. |
Materials for the experiment
- A 250 ml beaker of crushed ice (from a freezer at about −18 °C)
- A digital thermometer or temperature probe (−20 to 100 °C)
- A stirring rod and a stopwatch
- Optional: a beaker of warm tap water (about 40 °C) to stand the ice beaker in
- Graph paper or a spreadsheet
Safety: Use warm tap water only (no kettles or Bunsen burners). Handle freezer ice with a scoop or gloves. Wipe up spills.
Common misconceptions
| Pupils may think… | Actually… |
|---|---|
| Temperature and heat are the same thing. | Heat is energy transferred; temperature relates to average kinetic energy. |
| During melting the heat is 'lost'. | It goes into overcoming intermolecular attractions (latent heat). |
| All substances are densest as solids. | Water is densest at about 4 °C, and ice floats. |
Worksheet answers
- The energy supplied breaks or weakens the attractions holding particles in fixed positions; it does not increase their average kinetic energy, so the temperature stays constant until all the solid has melted.
- E = m·L = 200 × 2260 = 452,000 J (452 kJ).
- 6010 J/mol ÷ 18.0 g/mol ≈ 334 J/g.
- Rising, then flat at 0 °C, then rising again. Not perfectly flat: probe touching the beaker wall, uneven heating, poor stirring, heat from the room reaching the water unevenly.
Quiz answers
- According to kinetic theory, doubling the kelvin temperature of a gas… doubles the average kinetic energy of its molecules. Average kinetic energy ∝ kelvin temperature.[4]
- Why does the temperature stay at 0 °C while ice melts? The heat is used to overcome attractions between molecules. During a change of state the temperature remains constant.[3]
- Using 334 J/g, how much energy is needed to melt 50 g of ice at 0 °C? 16,700 J. E = m·L = 50 × 334 = 16,700 J.[3]
- Which needs more energy per gram for water? Boiling it away (about 2260 J/g). 40.67 kJ/mol against 6.01 kJ/mol.[3]
- Gas → solid directly is called… deposition. Sublimation is solid → gas; deposition is the reverse.[3]
- Why does ice float? Its density is about 9% lower than liquid water's. Water expands when it freezes.[5]
Going further
Add salt to crushed ice and record the temperature. Why do cities spread salt or grit on icy roads? Research and explain.
Sources used in this lesson
- [1] Chemistry: Atoms First, 1.2 Phases and Classification of Matter (OpenStax, Rice University): reliability High
- [2] Chemistry (OpenStax adaptation), 10.1 Intermolecular Forces (OpenStax Chemistry, hosted by Lumen Learning (CC BY 4.0)): reliability High
- [3] Chemistry, 10.3 Phase Transitions (OpenStax, Rice University): reliability High
- [4] Chemistry 2e, 9.5 The Kinetic-Molecular Theory (OpenStax, Rice University): reliability High
- [5] Water Density (U.S. Geological Survey, Water Science School): reliability High
Full list with links and a note on each source's reliability: echoesof.science/school/states-of-matter/sources/
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