Agriculture and Food 7–12 · Years 9–10

Energy content of foods by burning them under a can of water

Food Selection and Health

Practical, model not builtMedium risk

School laboratory, not for home

In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

This site has no interactive model of its own. Where a step or a material names a Concept Studio model, simulation or tool, it has not been built; an external simulation a step names (for example PhET) is not part of this site.

The idea

Burning a food releases its chemical energy as heat, and the temperature rise of a known mass of water gives a measured energy that can be compared with the nutrition information panel.

Safety card

Medium riskA teacher supervises

Setting: In a school laboratory, with a teacher supervising, under the school's risk assessment. Not for home.

Hazards

Bunsen flame and burning food
hot can and clamp
food allergens, especially nuts
smoke and pungent fumes from high-protein foods

Controls

eye protection throughout
no nuts or nut products
burn food over a heat-resistant mat
high-protein foods only in a fume cupboard
foods in the laboratory are never eaten

Note

Heat and flames: NSW Department of Education, Chemical Safety in Schools (CSIS) 2021 Technical Update: Section 1 (general information for all staff) and Volume 2 Appendix D (generic risk assessment advice for each chemical). Complete a CSIS or RiskAssess site-specific risk assessment before the lesson.

What you need

metal can calorimeter (or boiling tube) held in a stand and clamp over a heat-resistant mat
stirring thermometer reading -10 to 110 °C, 25 mL measuring cylinder
Bunsen burner, mounted needle and an old teaspoon for foods that melt
balance reading to 0.01 g
dry foods with nutrition information panels: mini marshmallows, popped popcorn, corn chips, dry pasta, bread (no nuts)
eye protection

How to do it

Measure 25 mL of water into the can, clamp it level and record the water temperature.
Weigh a piece of food, fix it on the mounted needle (or the teaspoon), light it in the Bunsen flame and hold it about 1 cm below the can.
Relight the food at once if it goes out. When it stops burning, stir and record the highest temperature.
Reweigh any unburnt food and calculate the mass burnt.
Calculate the heat taken in by the water and the energy per gram, and compare it with the panel value per gram.
Refill with fresh cold water and repeat three times for the class standard food and once for another food.

What you should see

Heating 25.0 g of water by 30.0 °C takes 3135 J; if 0.50 g of food was burnt, that is 6.27 kJ per gram, which is 36.9% of a panel value of 17.0 kJ per gram. The measured energy per gram is always well below the panel value because much of the heat escapes to the air, the can and the clamp; the RSC notes name the poor thermal conductivity of a glass boiling tube as a possible major cause of error and recommend a metal container held in a clamp. Foods with more fat per 100 g on their panel are expected to release more energy per gram in the test, because fat supplies 37 kJ per gram against 17 kJ for protein and carbohydrate. The learner knows it worked when three runs with the standard food agree closely and every result sits below the panel value.

What changes

What you change: food
What you measure: temperature rise of the water (°C), energy released per gram of food burnt (kJ/g)
What you keep the same: 25 mL of water
same can and clamp height (food 1 cm below)
starting water temperature
similar mass of food

Common misconceptions

Each of these ideas is wrong, and the activity is a chance to test it.

The can of water captures all the energy in the food.
The energy on a food label is the heat given off when the food is burned.
A food that burns with a bigger flame always contains more energy.

Curriculum references

The NSW syllabus outcomes and Australian Curriculum v9 codes this activity supports. They are references, not a verified or complete curriculum alignment.

Food Technology Years 7–10 Syllabus (2019)FT5-6 FT5-8
Food Technology 7–10 Syllabus (2025), new syllabus, implementation from 2028FT5-NSA-01
Australian Curriculum v9AC9S9U05

Sources

The pages the author read to write this activity.

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