1.) A compound is a thing that is composed of two or more (separate) elements.
2.) A compound cannot be separated easily, while its properties differ from where it originates from. It also is formed from chemical reactions.
3.) A pure substance, also known as chemical substance, is a material with constant composition and consistant properties.
4.) If a substance is not a pure substance, then it is an impure substance.
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The coefficient in a chemical formula represents the amount of each chemical present. The amount of a substance is measured in moles.
Increase in heat, molecules start to escape and it turns to vapor