Answer:
Application of heat to certain substances causes only physical changes in which no new substance or substances are formed. Application of heat to some substances causes chemical changes, or chemical reactions, in which one or more new substances are formed, with different properties from the original. Decomposition of water occurs during electrolysis, in which a current of electricity is passed through a solution containing a little sulfuric acid. An element is a pure substance that has never been converted to a simpler substance by chemical means. When two or more elements combine in a chemical change, they form a compound. A pure substance might either be an element or a compound. An impure substance consists of a mixture of two or more elements or compounds.
