Energy and entropy > combustion

‘Rockets’ are made by filling plastic fizzy drink bottles with a mixture of hydrogen gas and air. The rocket is launched by igniting the mixture with an electric spark, and will fly several metres. The rocket can be set up to fly tethered to a string or launched from a short section of drainpipe.

A large fizzy drink bottle, from which the base has been removed, is filled with hydrogen. The hydrogen is allowed to burn at a small jet in the stopper of the bottle. As the hydrogen-air mixture changes in composition, an explosive mixture is reached, which then explodes with a load bang.

A large tin fitted with a press-on lid and a glass chimney is filled with methane. The gas is lit at the top of the chimney. After a while the flame burns down the chimney and, as the methane-air mixture in the tin changes in composition, an explosive mixture is reached and the lid of the tin is blown off with loud bang.

The context of a fat-pan (chip-pan) catching fire is used to demonstrate the conditions required to start combustion, and how to put such a fire out safely.

This experiment compares the amounts of heat energy produced by burning various alcohols.

A mixture of alcohol and air in a large polycarbonate bottle is ignited. The resulting rapid combustion reaction, often accompanied by a dramatic ‘whoosh’ sound and flames, demonstrates the large amount of chemical energy released in the combustion of alcohols.

Test-tubes containing three different proportions of hydrogen and air are prepared and the gas mixtures ignited. The loudness of explosions (‘pops’) is noted and related, at least in part, to the amount of energy produced when the hydrogen is burnt. The mixture producing the loudest ‘pop’ is used to estimate the ratio in which hydrogen and oxygen combine.

A spectacular demonstration that shows the large energy changes that occur during the combustion of alcohols, and also illustrates the principle of the internal combustion engine.

Cornflour is sprayed into the flame of a candle burning inside a large tin can with the lid on. The resulting small explosion caused by rapid combustion of the cornflour blows the lid off the tin. The reaction dramatically illustrates the conversion of the chemical energy stored in foodsuffs into heat and other forms of energy. It can also be used to show the effect of surface area on the rate of chemical reaction