To be entirely general, all chemical changes or reactions are considered physical since all chemicals and their reaction products are physical. The converse of this is generally not true: most physical changes like bending a wire or lifting a block do not directly involve chemical changes. The wire and the block are chemically the same after the physical change.
An example of a chemical change that is obviously physical is the explosion of a mixture of gasoline and oxygen in air that propels most cars. The chemical reaction releases heat that causes the gasses to expand inside the cylinder and push the piston, ultimately rotating the crankshaft and finally the tires. The initial mixture of gasoline (a hydrocarbon) and oxygen are converted by the chemical reaction into water and carbon dioxide plus a number of undesirable pollutants including carbon monoxide, oxides of nitrogen and unburned hydrocarbons.
Answered by: Scott Wilber, President, ComScire - Quantum World Corporation
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