Susan Jensen, ape 13, of Sarasota, Florida, for her question:
What makes a candle flame hot?
A candle flame is caused by a chemical reaction called combustion. The same chemical activity takes place whenever oxygen combines with a fuel substance and changes it fast enough to give off heat and light. The oxygen required is right there in the air. The fuel may be any one of numerous burnable substances. Most of our candles use paraffin waxes extracted from petroleum. These waxes are made of small hydrocarbon molecules of methane, strum together in long polymer chains.
The basic ingredients are oxygen and fuel but one more item is needed to start the chemical activity. Every burnable substance has its own kindling point, a certain temperature at which it ignites. This is why a wick is stuffed down the center of a candle. We use a lighted match to ignite the top of the wick. As it burns it gradually melts the candle wax, which turns to vapor. The wick flame is warm enough to ignite the small plume of rising methane type gas.
Chemical reactions change substances by remodeling their molecules. Some use outside energy to do this and others release energy. Millions of years ago, forest greenery used energy from sunlight to build the complex hydrocarbon substances in our fossil fuels. When these are burned, chemical activity breaks these old molecules apart. This frees the captive solar energy that held them together which goes off as heat.
Candle wax is a storehouse of hydrogen and carbon atoms, tied in molecule packages with energy from long ago sunbeams. When it melts, the vapor burns and the chemical reaction breaks these packages apart. The released energy makes the flame hot. Some of the freed carbon and hydrogen atoms combine with oxygen in the air and form molecules of carbon dioxide and water vapor. As long as the fuel burns, its molecules keep changing and releasing their captive heat energy.
Christmas, of course, is for young persons, though Andy suspects that Old Santa enjoys it all as much as you do. In the 1800s, the great scientist Michael Faraday also figured out a way to enjoy his Christmases. He left the busy lab where he worked all year and went forth to explain the wonders of science to the children of London Tom. One of their favorite talks was called The Chemical History of the Candle.
Way back in 1831, Michael Faraday invented the dynamo that pointed the way to our electric generators. However, it took many years to set up the great power systems that make it possible to decorate our trees with electric lights. In Faraday's time, they used candles and sometimes their open flames burned down the tree and the whole house. Our update lights are as safe as modern experts can make them. Nevertheless, we need a sensible adult to check the wires for weak spots that can cause hot tempered short circuits.