Enthalpy of Combustion Virtual Lab: Alcohols and Heat Loss

This enthalpy of combustion virtual lab follows the classic spirit-burner practical of IB, A-level and Australian senior chemistry. Students weigh a spirit burner, heat 100 g of water in a copper can by about 20 °C and calculate ΔcH from q = mcΔT and n = Δm/M. They compare four alcohols with data-book values, find the change per CH₂ group and test ways to cut heat loss. Every value below was read from the simulation.

Curriculum links

• IB Diploma Chemistry (first assessment 2025): Reactivity 1.1, measuring enthalpy changes by calorimetry, and Reactivity 1.3, energy from fuels.
• AQA A-level Chemistry 3.1.4.2 (calorimetry) and required practical 2, measurement of an enthalpy change.
• NSW HSC Chemistry, Module 7 Organic Chemistry: the investigation comparing the enthalpy of combustion of a range of alcohols.
• VCE Chemistry Unit 3: energy from fuels and calorimetry.

Simulic is not affiliated with or endorsed by the IB, AQA, NESA or the VCAA.

Before the lab (5 min)

Ask students to commit to a prediction, on paper or as question 1 of the class link:

"The data-book enthalpy of combustion of ethanol is −1367 kJ/mol. How will your value from a spirit burner and a copper can compare?"

Many students expect a careful experiment to get close to the data book.

Method in the simulation

1. Keep View: Spirit burner: alcohols, Water 100 g, Flame gap 3.0 cm and Data set 1. Leave draught shield, lid on can and include heat taken by the copper can unticked.
2. Choose Fuel: methanol. Record m₁ and T₁ from the readout, then press Light.
3. When ΔT reaches about 20 °C, press Put out. Wait for the message that the temperature has passed its peak, then press Record.
4. Repeat steps 2–3 for ethanol, propan-1-ol and butan-1-ol, in that order.
5. For each run, calculate q = 100 × 4.18 × ΔT (J), n = Δm/M and ΔcH = −q/n. Then compare with the table.
6. Improvement test: choose ethanol, tick draught shield and do one more run. Use your own table: the sim adds this run to ethanol's mean.

Run	Alcohol	M (g/mol)	m₁ (g)	m₂ (g)	T₁ (°C)	T₂ (°C)	ΔcH (kJ/mol)
1	methanol	32.04
2	ethanol	46.07
3	propan-1-ol	60.10
4	butan-1-ol	74.12
5	ethanol + shield	46.07

Expected results

On data set 1, m₁ and T₁ are fixed for each run; Δm and ΔT depend on when you put the flame out.

Run	Alcohol	Δm (g)	ΔT (°C)	ΔcH (kJ/mol)	Data book	%
1	methanol	0.87	20.3	−312	−726	43
2	ethanol	0.63	20.0	−611	−1,367	45
3	propan-1-ol	0.53	20.6	−976	−2,021	48
4	butan-1-ol	0.55	20.5	−1,155	−2,676	43

• Worked example, ethanol: q = 100 × 4.18 × 20.0 = 8,360 J = 8.36 kJ; n = 0.63 / 46.07 = 0.0137 mol; ΔcH = −8.36 / 0.0137 = −611 kJ/mol.
• Trend: about −281 kJ/mol per CH₂ from methanol to butan-1-ol (the sim's fit: −289), less than half the data-book −654.
• Across data sets 1–12, runs of the sim's model gave ethanol −501 to −692 kJ/mol (38–50%).
• Improvements (ethanol): a draught shield gave 63% (run 5); shield and lid 61%. Ticking include heat taken by the copper can adds about 5%.

Questions for students

1. (Prediction, asked again after the lab) How will your ΔcH for ethanol compare with the data-book value?
2. Which is a control variable when you compare the four alcohols?
3. What is ΔcH of ethanol from your run?
4. By how much does ΔcH change per CH₂ group, from methanol to butan-1-ol?
5. Why is your value much smaller than the data book, and what improves it?

Answers for teachers: (1) Much less negative, about half (45% on run 2). (2) The mass of water and the flame gap. (3) Accept −720 to −480 kJ/mol (−611 on data set 1). (4) Accept −350 to −200 kJ/mol per CH₂ (−281 on data set 1). (5) Heat escapes to the air and the can; some fuel burns incompletely. A draught shield raised ethanol from 45% to 63% (run 5).

Common misconceptions

• "ΔcH is positive because the water gets hotter." Heat leaves the reaction, so ΔcH is negative.
• "Butan-1-ol heats the water more, so it releases more energy." Every run stopped at ΔT ≈ 20 °C; only the mass needed changed: 0.87 g of methanol, 0.55 g of butan-1-ol.
• "The closer the can, the better." Ethanol reached about 51% at 2.0 cm in our model runs, but 45% at 1.0 cm, with more soot.

Extension

• Flame gap: in our model runs, ethanol fell to about 32% at 5.0 cm and 19% at 8.0 cm.

FAQ

Can students calculate ΔcH without the sim doing it?

Yes. In the class link's starting values, tick Students calculate (hide results). The table then shows only masses and temperatures and the readout hides the means, though the ΔcH graph still plots each result.

Why do my students get slightly different numbers?

Each run's starting values and efficiency come from Data set (reproduces the same runs) and the run number. The ranges for questions 3 and 4 hold for data sets 1–12 and any run order.

What if a student records before the peak?

The sim warns that T₂ may be too low. Ask them to repeat the run: recording early makes ΔcH less negative.

Related simulations and guides

Calorimetry – Enthalpy of Neutralization of HCl + NaOH Bond enthalpies – calculating ΔH of a reaction

For calorimetry in solution, see the calorimetry virtual lab. For an enthalpy change found indirectly, see the Hess's law virtual lab.