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January 29 th marks the passing of Fritz Haber. Haber was a German chemist who discovered a process to create ammonia from atmospheric gases. The Haber-Bosch process is a reaction that fixes nitrogen to form ammonia (NH 3 ) from nitrogen gas (N 2 ) and hydrogen gas (H 2 ) under pressure over an iron catalyst. Haber discovered the process on a laboratory scale using table top equipment. German chemical engineer Carl Bosch converted the laboratory equipment to be used on large scale industrial equipment. This process was important in the production of agricultural fertilizers to replace the guano industry of South America. During World War I, the process was important to Germany for the production of munitions and explosives. The process would earn both Haber and Bosch Nobel Prizes in Chemistry (1918 and 1931 respectively). Today, the Haber-Bosch process accounts for 100 million tons of fertilizer per year.

How well can you distinguish between physical and chemical changes? Physical changes involve a change in the form of a substance, but it remains the same on the molecular level. On the other hand, chemical changes involve chemical reactions. New products are created, often accompanied by changes in temperature or color. Melting the wax of a candle is an example of a physical change. The wax only changes shape -- it's still wax. Burning a candle is a chemical change. The wax undergoes a chemical reaction, producing carbon dioxide and water. Do you think you understand? Here's a quick self-test you can take to check whether you can tell the two types of changes apart... Try the quiz