Why is the cap put back on the spirit burner straight after heating?

To stop the alcohol evaporating before reweighing

Why are the measured energy values lower than data book values?

Heat is lost to the surroundings and combustion may be incomplete

Core practical: the heat from burning alcohols

Core practical 9.28 compares the temperature rise produced by burning different alcohols.

GCSE · 1CH0 · 9.26, 9.27, 9.28 (Chemistry only)
About 16 minutes

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The first five alcohols

Alcohols contain the -OH functional group. General formula C_nH_2n+1OH.

Alcohol	Formula
Methanol	CH₃OH
Ethanol	C₂H₅OH
Propanol	C₃H₇OH
Butanol	C₄H₉OH
Pentanol	C₅H₁₁OH

The method

1. Measure 100 cm³ of water into a copper can (calorimeter) clamped above a spirit burner. Record the water temperature.
2. Weigh the spirit burner with its cap on.
3. Light the wick and heat the water, stirring, until the temperature has risen by a set amount (for example 20 °C).
4. Put the cap on to put out the flame, and reweigh the burner.
5. Repeat for each alcohol, keeping the volume of water, distance to the flame and temperature rise the same.
Use a draught screen to reduce heat loss.

Comparing the alcohols

energy transferred to the water (J) = mass of water (g) × 4.2 × temperature rise (°C)
Divide by the mass of alcohol burned to find the energy per gram.
Compare the alcohols with a bar chart. The energy released per mole increases as the chain gets longer, because there are more bonds to break and make.
Results are lower than data book values because of heat loss and incomplete combustion.

Worked example

Burning 0.80 g of ethanol raises the temperature of 100 g of water by 20 °C. Calculate the energy per gram of ethanol in kJ/g.

Energy = 100 × 4.2 × 20 = 8400 J
Per gram = 8400 ÷ 0.80 = 10 500 J/g
= 10.5 kJ/g

Answer: 10.5 kJ/g

Key idea

Alcohols have the -OH group: methanol CH₃OH up to pentanol C₅H₁₁OH. Weigh the spirit burner before and after heating a fixed mass of water by a set amount. Energy = mass of water × 4.2 × temperature rise; divide by mass of alcohol burned.

Key words

Group: A vertical column of the periodic table. Elements in a group have the same number of outer electrons and similar reactions.
Functional group: The group of atoms that gives a homologous series its typical reactions, such as C=C, -OH or -COOH.
Mole: The amount of substance containing 6.02 × 10^{23} particles. Its mass in grams equals the A_{r} or M_{r}.
Incomplete combustion: Burning with not enough oxygen, producing carbon monoxide and/or carbon (soot), and water. Carbon dioxide may also form.

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Quick check

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Extra practice

2 more questions

Try each one, then tap to check.

100 g of water is heated by 25 °C. Calculate the energy transferred in J. (c = 4.2 J/g °C)
Show the answer
Answer: 10500 J
Q = 100 × 4.2 × 25 = 10 500 J
8400 J is transferred by burning 0.30 g of ethanol. Calculate the energy per gram in J/g.
Show the answer
Answer: 28000 J/g
8400 ÷ 0.30 = 28 000 J/g

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Sources and references

Checked by the GCSE-ready editorial team, 17 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

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