Enthalpy of combustion – spirit-burner calorimetry, food energy, bomb calorimeter and fuel comparison
ChemistryEnergetics & ThermodynamicsAges 15–16
Loading…
Sign in to playA virtual practical: burn methanol, ethanol, propan-1-ol, butan-1-ol and pentan-1-ol in a spirit burner under a copper can of water, weigh the burner before and after, read the highest temperature, and calculate q = mcΔT, n = Δm/M and ΔcH = −q/n. Compare with data-book values (−726 to −3329 kJ/mol) to quantify heat loss and the trend of about −654 kJ/mol per CH₂ group. Further views burn a food sample under a boiling tube, calibrate a bomb calorimeter electrically (CF = VIt/ΔT), and compare the specific energy, energy density and CO₂ output of diesel, biodiesel, petrol, bioethanol, natural gas, biogas and hydrogen.
Lesson: Enthalpy of combustion of alcohols – calorimetry practical and energy from fuels
What it shows
This virtual practical measures the enthalpy of combustion of the first five straight-chain alcohols. Students weigh a spirit burner, heat a copper can of water by about 20 °C, record the highest temperature and calculate ΔcH from q = mcΔT and n = Δm/M. Results typically reach only 40–70 % of data-book values, so the sim invites discussion of heat loss, incomplete combustion and improvements such as a draught shield or lid. A results table, repeat runs and a ΔcH-against-chain-length graph reveal the steady change per CH₂ group. Extra views cover food energy, electrical calibration of a bomb calorimeter and a comparison of fossil fuels, biofuels and hydrogen.
How to use
Choose a Fuel, the mass of Water and the Flame gap, and tick draught shield or lid if wanted. Press Light, then Put out when the temperature has risen about 20 °C; wait for the peak and press Record. Repeat runs and change fuels to fill the table and graph. Use Speed to run faster and Data set to reproduce the same results. Other views let you burn food, calibrate the bomb calorimeter or compare fuels.
Parameters you can change
- View Spirit burner: alcohols, Burning a food sample, Bomb calorimeter, Comparing fuels
- Fuel (alcohol) methanol, ethanol, propan-1-ol, butan-1-ol, pentan-1-ol
- Mass of water in the copper can 50–250 g
- Distance from the flame to the base of the can 1–8 cm
- Use a draught shield
- Put a lid on the can
- Include the heat taken by the copper can
- Students calculate (hide results)
- Data set (reproduces the same runs) 1–999
- Food sample peanut, half a cashew nut, piece of potato crisp, marshmallow
- Quantity compared Specific energy (MJ/kg), Energy density (MJ/L), CO₂ released per MJ
Questions to explore
- Why is the enthalpy of combustion measured with a spirit burner much smaller than the data-book value?
- By how much does ΔcH change for each extra CH₂ group, and why is the change almost constant?
- Why does a bomb calorimeter give results much closer to data-book values than a copper can?
