Heat combustion of alcohols Thermochemistry Heat combustion of alcohols

Today’s focus Determine experimentally which of the three alcohols methanol, ethanol, and propan-1-ol would be the best alternative to petrol by obtaining their heats of combustion.

Complete combustion of alcohols Alcohols burn readily in the presence of oxygen with a non-smoky flame to form CO2 and H2O Example (Ethanol) C2H5OH + 3 O2 → 2 CO2 + 3 H2O(l) (ΔHc = −1364 kJ/mol) Heat energy is released so exothermic

Experiment Heating water to get ΔT (Remember the specific heat capacity of water is 4.184 J/g/degrees Celsius) From this we can work out ΔE (ΔE = m x ΔT x 4.184) Calculate the mass of alcohol burnt, and therefore the energy released per gram. Finally calculate the heat of combustion in kJ/mol Practical- page 147 of prac book Work in pairs Safety glasses to be worn!!!!

Fermentation Ethanol fermentation, also referred to as alcoholic fermentation, is a biological process in which sugars such as glucose, fructose, and sucrose are converted into cellular energy and thereby produce ethanol and carbon dioxide as metabolic waste products. Because yeasts perform this process in the absence of oxygen, ethanol fermentation is classified as anaerobic. Ethanol fermentation occurs in the production of alcoholic beverages and ethanol fuel, and in the rising of bread dough. C6H12O6 → 2C2H5OH + 2CO2

So where to for alcohols as fuels? The proposed alcohol to replace current fossil fuels will be produce through fermentation (biofuel). 1st generation biofuel is produced from feedstock, such as sugarcane and maize. Implications? 2nd generation biofuel is produced from non-food crops. Implications? 3rd generation biofuel is produced from algae (sewage plants). Called algaeculture. Suggested that the area required to produce enough ethanol form ‘algae ponds’ would be 7 times less than if it was produced from 1st generation techniques. Two ways in which ethanol can be produced from algae?