Question

Define a physical change and chemical change

Answer 1

A physical change in a substance doesn't change what the substance is.
In a chemical change where there is a chemical reaction, a new substance is formed and energy is either given off or absorbed.

Answer 2

Physical changes are changesaffecting the form of a chemicalsubstance, but not its chemicalcomposition. Physical changes are used to separate mixtures into their component compounds, but can not usually be used to separate compounds into chemical elements or simpler compounds.Chemical changes occur when a substance combines with another to form a new substance, called chemical synthesis or, alternatively, chemical decomposition into two or more different substances. These processes are called chemical reactions and, in general, are not reversible except by further chemical reactions.