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SCX Chemistry · Chapter 6: Specific energy and comparing fuels

Year 11 SCX · About 15 minutes with activities · Turn your sound on

Chapter 6 · Specific energy
Ethanol: 1.5 g burnt300 g of water
Propane: 1.1 g burnt200 g of water
e = 37 800 J g⁻¹ethanol
e = 45 600 J g⁻¹propane
Energy from the fuelis caught by the water
Water heats uptemperature rises
ThermometerΔT = final − initial
Can of watermass of water, m, for q = mcΔT
Balancefuel burnt = before − after
Ethanol: blue flameno residue
Propane: yellow flameblack residue on the can
CO₂ + H₂Ocomplete combustion
CO₂ + H₂O + CO + Cincomplete combustion
CO and soot harmCO binds to haemoglobin · soot irritates lungs

Chapter 6 recap

  • q = mcΔT: q = heat energy (J), m = mass of water heated (g), c(water) = 4.18 J g⁻¹ °C⁻¹, ΔT = final − initial temperature (°C).
  • e = q/m: specific energy, the energy released per gram of fuel burnt (J g⁻¹). Here m = mass of fuel burnt = mass before − mass after.
  • Comparing fuels: propane 45 600 J g⁻¹ > ethanol 37 800 J g⁻¹, but propane’s yellow, sooty flame means CO and C. Ethanol burns cleanly and is renewable, so it is better overall.
  • Next: Chapter 7 · Moles, particles and stoichiometry

Which fuel gives the most energy per gram?

Chapter 6 · About 15 minutes · sound on

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