Physics 11–12 · Year 11
Latent heat of fusion: ice in water calorimetry and a stearic acid cooling curve (syllabus practical)
Module 3: Waves and Thermodynamics (Thermodynamics)
School laboratory, not for home
In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
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The idea
During a change of state energy is transferred without a change of temperature, and that hidden energy per kilogram is the latent heat.
Safety card
Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.
Hazards
- hot water bath and hot plate
- hot stearic acid
- glass boiling tube
Controls
- tongs and heat mat
- safety glasses
- do not heat stearic acid over a flame
Note
Chemicals and heat: record the activity in RiskAssess (https://www.riskassess.com.au/) using its safety data for each chemical, and apply the NSW Department of Education Chemical Safety in Schools package; Science ASSIST risk management sheet https://asta.edu.au/resource/ais-risk-management-and-risk-assessment/.
What you need
- Polystyrene cup, 0.200 kg of water at about 25 degrees, ice cubes dried on paper towel (about 50 g), thermometer to 0.1 degree, electronic balance
- Cooling curve: boiling tube of stearic acid, water bath on a hot plate, thermometer or temperature probe with data logger, stopwatch (the NSW Department of Education Module 3 guide, Activity 15)
How to do it
- Weigh the cup with water; record its temperature.
- Add the dried ice, stir until it has all melted and record the lowest temperature reached; reweigh to find the mass of ice.
- Energy balance: water cooling = ice melting + meltwater warming; solve for the latent heat of fusion.
- Cooling curve: warm the stearic acid to about 80 degrees in the bath, remove, and record the temperature every 30 s while it cools and solidifies.
- Identify the plateau and relate the constant temperature to energy still leaving the tube.
What you should see
Adding 50 g of ice at 0 degrees to 200 g of water at 25.0 degrees gives a final temperature of 4.0 degrees Celsius with the accepted latent heat 334 kJ/kg; when the latent heat is solved from a measured final temperature, each 0.5 degree error in that temperature shifts the result by 10.5 kJ/kg, about 3 per cent. The stearic acid curve falls, holds flat for several minutes while it solidifies, then falls again.
What changes
- What you change
- mass of ice added
- What you measure
- final equilibrium temperature
- What you keep the same
- mass and starting temperature of the water
- ice at 0 degrees and dried
- insulated cup
Common misconceptions
Each of these ideas is wrong, and the activity is a chance to test it.
- Ice at 0 degrees and water at 0 degrees hold the same energy; the water holds 334 kJ more per kilogram.
- The temperature keeps falling during freezing; it holds steady until freezing is complete.
Curriculum references
The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.
Sources
The pages the author read to write this activity.
- www.nsw.gov.au/sites/default/files/noindex/2025-03/physics-stage-6-syllabus-2017.docx
- education.nsw.gov.au/content/dam/main-education/teaching-and-learning/curriculum/key-learning-areas/science/s-6/physics/Physics-module-3-guide.docx
- hyperphysics.gsu.edu/hbase/Tables/phase.html
- hyperphysics.gsu.edu/hbase/Tables/sphtt.html