1# Chemical energy 2 3Chemical energy = heat content = enthalpy 4 5$$\Delta H = H_{\text{products}} - H_{\text{reactants}}$$ 6 7**Exothermic** - energy released from system 8**Endothermic** - energy absorbed by system 9 10Must specify states (latent heat) 11 12## Thermochemical equations 13 14$\Delta H$ notates energy change (i.e. kJ / mol) 15Exothermic - negative $\Delta H$ 16 17## Calorimetry 18 19$$E = mc \Delta T$$ 20 21$$\text{calibration factor} = {E \over \Delta T} = {VIt \over \Delta T} \quad \text{J/K}$$ 22 23## Fuels 24 25Substance used for energy production by **combustion** (exothermic) 26Fossil fuels - decaying organic material (e.g. coal, petrol, nat. gas) 27 28Crude oil - mixture of alkanes 29Derivatives: 30 31- petrodiesel (12-24 carbons / molecule) 32- LPG 33- nat. gas 34 35### Efficiency 36 37$$\text{% efficiency} = {\text{energy obtained in desired form} \over \text{energy available before conversion}} \times 100$$ 38 39### Refining crude oil 40 41**Fractional distillation** - liquid is separated based on boiling point. B.P $\propto$ molecular size. 42 431. Separation column has temperature gradient (cooler at top) 442. Crude oil is heated and injected at base 453. Some components vapourise and rise 464. When they reach $h$ where $T_{\text{ambient}}(h)=T_{\text{boiling}}$, they condense 475. Trays catch falling condensed liquid 48 49 50 51### Biodiesel 52 53- made from animal & plant fats 54- fats are esters between carboxylic acids (fatty acids) and glycerol. 55- produced by reacting fats (triglycerides) with alcohol