The Use of Ethanol as a Fuel


Students learn to outline the use of ethanol as a fuel and explain why it can be called a renewable resource

At high temperatures in the presence of oxygen, all organic compounds will decompose to give carbon dioxide and water . This process is called combustion, and is usually accompanied by cheery flames and loud noises that many of us find rather pleasing... (The yellow colour of a flame comes from the fluorescence of incompletely burned pieces of carbon)

The reaction of sucrose with oxygen produces identical amounts of carbon dioxide and water whether it is burnt or metabolised inside an animal. Though the same amount of energy is released overall, the detailed pathways of the reactions are very different - a disciplined series of enzyme-mediated steps in biological systems, a chaotic cascade of free-radical reactions in a flame.

One of our researchers having far too much fun blowing things up...

Ethanol can burn nicely, is as safe to handle and transport as petrol, if not more so, and can be used in internal combustion engines without requiring extreme redesign. As far back as the beginning of last century, the Model T Ford was designed to operate on ethanol (for more info see:,

The chemical reaction for the combustion of ethanol is given below - each molecule is drawn out in full, to make it clear where all the carbon and hydrogen in the ethanol ends up.

The combustion of ethanol

This generates 1409.4 kilojoules of heat per mole of ethanol. Since the molecular weight of ethanol is about 46 g and about 4.2 joules can raise the temperature of one gram of water by one degree, this means that - hmm - 8 × 7 is 56 - where's the decimal place gone - er - the combustion of one gram of ethanol could raise 90 g of water from 20 °C to 100 °C, assuming all of the heat generated can be channeled into heating the water. This is not too bad, and might go some way toward explaining why many Russians imbibe dilute ethanol solutions on frosty nights. (And frosty mornings, and mid afternoons)

So ethanol has the potential to release quite a bit of energy when it's burnt. This means that ethanol has the potential to be a quite useful fuel. One of the other nice things about using ethanol (as we will see later) is that the presence of oxygen within the fuel itself (i.e. the O in the OH group) leads to cleaner combustion and less soot formation. This is quite a nice advantage.

The other things about ethanol is that it can be considered to be a renewable resource. Later on, we'll look at the energy costs of making from plant matter and using that as a fuel on a widespread basis. At the moment, though, we can already see that if we're making ethanol out of plant matter, and plant matter is considered to be a renewable resource then ethanol from plants is a renewable resource.

So will ethanol save us from chaos when we run out of oil? Keep reading and we'll try to draw some more conclusions in the final section of this trail.