1.3 Energy from fuels

Objective notes

9 learning objectives

1.3.1Combustion reactions

• Reactive metals, non-metals, organic compounds + O₂

• Deduce complete combustion equations for hydrocarbons and alcohols

1.3.2Incomplete combustion

• Produces CO and C

• Deduce incomplete combustion equations for hydrocarbons and alcohols

1.3.3Fossil fuels

• Coal, crude oil, natural gas

• CO₂ emissions and greenhouse effect

• Compare fuels by carbon dioxide released and energy output

1.3.4Biofuels

• From biological carbon fixation (photosynthesis)

• Renewable vs. non-renewable

• Consider advantages and disadvantages of biofuels compared with fossil fuels

1.3.5Fuel cells

• Convert chemical energy directly to electrical energy

• Half-equations for electrode reactions

• Include hydrogen and methanol fuel cells; PEM details are not assessed

1.4.1(HL)—Entropy (S)

• Measure of dispersal of matter/energy

• More energy distributions = higher entropy

• Order: Sgas > Sliquid > Ssolid

• Calculate ΔS⦵ from S⦵ values

1.4.2(HL)—Gibbs energy (ΔG)

• ΔG⦵ = ΔH⦵ − TΔS⦵

• Relates energy from reaction to ΔH, ΔS, T

1.4.3(HL)—Spontaneity

• Spontaneous when ΔG < 0

• Temperature at which reaction becomes spontaneous

• Interpret signs of ΔG from thermodynamic data

1.4.4(HL)—Equilibrium and Gibbs energy

• At equilibrium: ΔG = 0

• ΔG = ΔG⦵ + RT ln Q

• ΔG⦵ = −RT ln K

• Link ΔG, Q, and K to reaction direction and equilibrium position