Investigating State Changes

Overview

In this 80-minute lesson, students build on earlier lessons in the unit by using particle models to explain observable changes of state. They focus on evaporation and condensation, linking the motion/arrangement of particles to what they can see, measure, and predict.

Learning intentions

• Students will model particle behaviour to explain evaporation and condensation.
• Students will observe evidence of evaporation and condensation in a simple, safe investigation.
• Students will plan and conduct a fair test (with support) and record measurements accurately.
• Students will compare their results with predictions and identify possible sources of error.

Success criteria

• I can describe evaporation as a change where liquid particles spread and move into the air.
• I can describe condensation as a change where water vapour particles come together to form liquid droplets.
• I can use evidence from observations (e.g. droplet size/amount, time taken) to support my conclusion.
• I can explain at least one reason my results might be different from others in the class.

Curriculum links

• Science — AC9S5U04: explain observable properties of solids, liquids and gases by modelling the motion and arrangement of particles.
• Science — AC9S5I01: pose investigable questions to identify patterns and test relationships and make reasoned predictions.
• Science — AC9S5I02: plan and conduct repeatable investigations, including variables, control of fair tests, safety, and record methods.
• Science — AC9S5I03: use equipment to observe, measure and record data with reasonable precision.
• Science — AC9S5I05: compare methods/findings, recognise possible sources of error, and draw reasoned conclusions.

Lesson structure (80 minutes)

1. 0–10 min · Hook: “Why does it disappear?”

• Teacher displays two jars/bowls: one with a small amount of water in open air and one covered (e.g. cling film with a small hole), plus a short prompt: “What changes and where does the water go?”
• Students turn-and-talk: write one prediction about what will happen to the water in each container, using words like “liquid”, “air”, “vapour”, “droplets”.

2. 10–25 min · Direct teach: particle model role-play

• Teacher leads a quick particle model using students as particles: “liquid particles” packed closely, “gas particles” spread out and move faster.
• Students act out:
• Evaporation: some “liquid particles” gain energy, break away, and spread into the “air” space.
• Condensation: “gas particles” lose energy when near a cooler surface and gather into droplets.
• Whole-class checks: Teacher asks, “What are we modelling—movement, arrangement, or both?”

3. 25–45 min · Guided investigation: condensation evidence

• Teacher sets up a repeatable station for groups: a clear cup/jar with warm water (teacher-prepared if needed), covered with a lid or plastic wrap; ice placed on top so students can observe droplets forming on the underside.
• Students (in groups of 3–4) record a simple table:
• Start time (minute/second), end time when droplets clearly appear.
• Observations: number of droplets or “light/mid/heavy” condensation, and where droplets form (edges vs centre).
• Teacher circulates, checking fair-test decisions: only change the variable being tested (e.g. temperature of the surface using “more/less ice” or “same ice for each trial”), while keeping cup size and water amount the same.
• Safety reminder: no tasting, care with warm water, ice handled with gloves/towel if required.

4. 45–60 min · Fair test planning (quick method refinement)

• Teacher provides two possible questions on the board, students choose one:
• “How does surface cooling (more/less ice) affect how quickly condensation forms?”
• “How does water temperature affect when droplets appear?”
• Students draft a brief method (3–4 dot points): variable to change, measure/record, and what to keep the same; include a predicted outcome using particle language.
• Teacher confirms the plan is repeatable (same procedure each group).

5. 60–72 min · Compare and reason: evidence to conclusion

• Groups share one key result and one observation detail.
• Teacher guides students to recognise sources of error: timing differences, uneven ice contact, amount of water variation, visibility of droplets, measuring “first visible droplets” subjectivity.
• Students complete a short reasoning statement: “Our prediction was/was not supported because…”

6. 72–80 min · Exit ticket

• Students answer:
• “In one sentence, explain evaporation and condensation using particle language.”
• “Name one possible source of error in our investigation.”

Resources

• Clear cups/jars, lids or cling film/plastic wrap
• Ice (teacher-prepared quantities) and towels/gloves as needed
• Warm water prepared safely by teacher (or room-temperature water if required)
• Stopwatches or classroom timers
• Measuring jug or cup (to standardise water volume)
• Data tables (printed) for time and condensation observations
• Marker pens, whiteboard/markers
• Role-play particle cards or simple labels: liquid, gas, cool surface
• Safety signage and reminder cards (no tasting, careful handling)

Assessment

• Teacher observation checklist during modelling: correct use of “particles moving/spreading/gathering” when describing changes of state.
• Review group data tables for reasonable precision in timing and clear, observable descriptions.
• Exit ticket used to assess correct explanations of evaporation and condensation and identification of a plausible error.

Differentiation

• Support:
• Provide sentence starters: “Evaporation happens when…”, “Condensation happens when…”, “We measured…”, “A possible error is…”
• Use visual aids: particle diagram cards (liquid packed / gas spread / droplets forming).
• Assign roles in groups (timer, recorder, equipment manager) to ensure all students contribute.
• Extension (advanced learners):
• Challenge students to estimate/compare droplet rate using an additional measure (e.g. time to reach “heavy condensation”).
• Ask: “What real-world factors would affect condensation in homes (humidity, temperature, airflow)?” and require a particle-based explanation.
• EAL/SEN:
• Pre-teach key terms (evaporation, condensation, vapour, droplets, cool surface) with gestures and examples.
• Allow oral explanation to complement written exit ticket where appropriate.