Substance used for energy production by **combustion** (exothermic)
Fossil fuels - decaying organic material (e.g. coal, petrol, nat. gas)
+Crude oil - mixture of alkanes
+Derivatives:
+
+- petrodiesel (12-24 carbons / molecule)
+- LPG
+- nat. gas
+
### Efficiency
-$$\text{% efficiency} = {\text{energy obtained in desired form} \over \text{energy available before conversion}} \times 100$$
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+$$\text{% efficiency} = {\text{energy obtained in desired form} \over \text{energy available before conversion}} \times 100$$
+
+### Refining crude oil
+
+**Fractional distillation** - liquid is separated based on boiling point. B.P $\propto$ molecular size.
+
+1. Separation column has temperature gradient (cooler at top)
+2. Crude oil is heated and injected at base
+3. Some components vapourise and rise
+4. When they reach $h$ where $T_{\text{ambient}}(h)=T_{\text{boiling}}$, they condense
+5. Trays catch falling condensed liquid
+
+
+
+### Biodiesel
+
+- made from animal & plant fats
+- fats are esters between carboxylic acids (fatty acids) and glycerol.
+- produced by reacting fats (triglycerides) with alcohol
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