Fermentation of glucose to ethanol

Yeast converts glucose dissolved in water into ethanol and carbon dioxide. This process is called fermentation. The ethanol remains in the solution, while carbon dioxide is released as a gas.

Fermentation takes place in the absence of oxygen at a temperature of $$25\text{–}35,^{\circ}\mathrm{C}$$. The overall reaction is:

The equation shows that one glucose molecule forms two ethanol molecules and two carbon dioxide molecules.

Catalytic hydration of ethene

Ethanol is produced by reacting ethene with steam in the presence of an acid catalyst. This reaction is called hydration because water is added to ethene.

The reaction takes place at approximately $$300,°\mathrm{C}$$ and $$6000,\mathrm{kPa}$$, or about $$60,\mathrm{atm}$$.

Hydration is an addition reaction: the carbon–carbon double bond in ethene opens, allowing a hydrogen atom and an $$\ce{OH}$$ group from water to add across the bond. The product is ethanol.

The acid catalyst speeds up the reaction and is not used up overall.

Combustion of ethanol

Ethanol burns by reacting with oxygen, releasing energy to the surroundings. When there is enough oxygen for complete combustion, the products are carbon dioxide and water.

The balanced equation shows that one molecule of ethanol reacts with three molecules of oxygen to produce two molecules of carbon dioxide and three molecules of water. The atoms are rearranged: the number of atoms of each element is the same on both sides.

Uses of ethanol

Ethanol has two uses that depend on different properties: it can dissolve substances, and it can burn.

Ethanol as a solvent

Liquid ethanol is used as a solvent because other substances can dissolve in it. The dissolved substance spreads through the ethanol to form a solution.

Ethanol as a fuel

Ethanol is used as a fuel because it burns, releasing energy that can be used for heating. Its use as a fuel depends on its ability to burn, rather than its ability to dissolve substances.