Later, in the Seventeenth Century, a German chemist named George Ernst Stahl was the first to speak of chemical reaction, specifically, combustion. He said that a substance called phlogiston escaped into the air from all substances during combustion. He said that a burning candle would go out if a candlesnuffer was put over it because the air inside the snuffer became saturated with phlogiston. According to Stahl, wood is made up of phlogiston and ash, because only ash is left after combustion. His ideas soon brought speculations of doubt. When metal is burned, its ash has a greater mass than the original substance. Stahl tried to cover himself by saying that phlogiston will take away from a substance's mass or that it had a negative mass, which weren't relevant to his original theories.

In the Eighteenth Century Antoine-Laurent Lavoisier, in France, discovered an important detail in the understanding of the chemical reaction combustion of oxygen. He said that combus

John Dalton, in the early Nineteenth Century, discovered the atom. It gave way to the idea that a chemical reaction was actually the rearrangement of groups of atoms called molecules. Dalton also said that the appearance and disappearance of properties meant that the atomic composition gave the appearance of different properties. He also came up with idea that a molecule of one substance is exactly the same as any other molecule of the same substance.

Exoergic, or exothermic, reactions release energy during the reaction. Combustion is one of the major reactions that do this. The burning of wood, or any other fuel, gives off heat, and the burning of glucose in our bodies gives off both energy and heat.

Endoergic, or endothermic, reactions absorb energy during the reaction. The melting of an ice cube is an example of an endothermic reaction.

Scientists are playing with chemical reactions. In April of 1995, a chemist named Peter Schultz and a physicist named Paul McEuen of the University of California at Berkley announced that they could control chemical reactions molecule by molecule. "The key to the technique is to put a dab of platinum on the microscopic tip of an atomic force microscope. (The tip of such a microscope is a tiny cantilever that rides like a phonograph needle just above the s

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