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Chemistry 11–12 · Year 12

Comparing the enthalpy of combustion of methanol, ethanol, propan-1-ol and butan-1-ol by calorimetry

Module 7: Organic Chemistry

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

Each CH2 unit added to an alcohol adds a nearly constant amount of combustion energy per mole, and the energy per gram rises along the series as the oxygen fraction falls.

Safety card

Medium riskLearners carry it out, with a teacher supervising

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

Hazards

  • all four alcohols flammable; methanol toxic
  • hot can
  • refilling burners

Controls

  • burners filled by the technician and capped between runs
  • cap to extinguish
  • eye protection, hair tied back
  • well-ventilated room

Note

NSW Department of Education Chemical Safety in Schools (CSIS) package, 2021 Technical Update: Section 1.7 (risk assessment) and Volume 2 Appendix D (generic assessment advice and DoE chemical categories); record a RiskAssess (riskassess.com.au) risk assessment before the lesson and check the school's hazardous chemical register (CSIS Section 1.9) for local restrictions.

What you need

  • Spirit burners with caps containing methanol, ethanol, propan-1-ol and butan-1-ol (one each), labelled
  • Copper or aluminium can with 100.0 mL water, retort stand and clamp, draught shield
  • Thermometer to 0.1 degrees Celsius or a temperature probe, balance to 0.01 g, 100 mL measuring cylinder

How to do it

  1. Set the can 2 cm above the wick inside the draught shield; measure 100.0 mL of water into it and record its temperature.
  2. Weigh the capped burner, light it, and heat until the water has risen by 20.0 degrees Celsius; cap it and record the maximum temperature; reweigh.
  3. Repeat for each alcohol with fresh water at the same starting temperature; keep the same can, height and shield.
  4. Calculate the heat gained by the water, the moles of alcohol burned and the enthalpy of combustion for each; plot enthalpy against carbon number and draw the line of best fit.
  5. Calculate the percentage of the accepted value captured for each alcohol and comment on whether the ranking is reliable even though the absolute values are low.
  6. In the simulation compare the ideal temperature rise with the measured for each alcohol and read the increment per CH2.

What you should see

Accepted values (NIST WebBook): methanol 726, ethanol 1368, propan-1-ol 2021, butan-1-ol 2670 kJ/mol, an increment of about 650 kJ/mol per CH2; per gram 22.6, 29.7, 33.6, 36.0 kJ/g. With full heat capture 0.50 g of each would warm 100 g of water by 27, 36, 40 and 43 degrees Celsius. If the calorimeter captures between 30 and 60 percent of the heat, the class reports 218 to 435, 410 to 821, 606 to 1213 and 801 to 1602 kJ/mol; with the same can, height and shield for every alcohol the straight-line trend and the nearly constant increment still show. Soot increases along the series.

What changes

What you change
the alcohol (carbon number)
What you measure
enthalpy of combustion measured (kJ/mol) and energy per gram (kJ/g)
What you keep the same
  • water mass
  • temperature rise
  • can, height and shield
  • same starting temperature

Common misconceptions

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

  • Each extra CH2 adds the same energy per gram (per gram the energy rises from 22.6 to 29.7, 33.6 and 36.0 kJ/g, gaining less at each step, because the oxygen already in the molecule is a shrinking share of the mass).
  • The measured values being low means the accepted values are for a different reaction (they are the same reaction; heat escaped the calorimeter).
  • More soot means more energy was released (soot is unburned carbon, so less energy was released than complete combustion would give).

Curriculum references

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

  • Chemistry Stage 6 Syllabus (2017), NESA; the current syllabus, taught in 2026 (codes read from the syllabus document)CH12-14CH11/12-5CH11/12-6
  • Chemistry Stage 6 Syllabus (2017), NESA; the current syllabus, taught in 2026 (codes read from the syllabus document); a Working Scientifically outcome not among those the syllabus targets in Module 7, which it allows in any moduleCH11/12-3
  • Chemistry 11-12 Syllabus (2025), NESA; implemented from 2028, not yet taughtCH-12-03CH-12WS-03CH-12WS-05
  • Australian Curriculum v9No Australian Curriculum v9 code is listed.

Sources

The pages the author read to write this activity.

  1. www.nsw.gov.au/education-and-training/nesa/curriculum/science/chemistry-stage-6-2017
  2. www.nsw.gov.au/sites/default/files/noindex/2025-03/chemistry-stage6-syllabus-word.docx
  3. curriculum.nsw.edu.au/learning-areas/science/chemistry-11-12-2025/outcomes
  4. edu.rsc.org/experiments/comparing-heat-energy-from-burning-alcohols/1733.article
  5. edu.rsc.org/practical/enthalpy-change-of-combustion-of-ethanol-practical-videos-14-16-years/4018539.article
  6. webbook.nist.gov/cgi/cbook.cgi?ID=C71363&Mask=2
  7. webbook.nist.gov/chemistry

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