<P> Chemical substances exist as solids , liquids , gases , or plasma , and may change between these phases of matter with changes in temperature or pressure . Chemical substances may be combined or converted to others by means of chemical reactions . </P>
<P> Chemical substances exist as solids , liquids , gases , or plasma , and may change between these phases of matter with changes in temperature or pressure . Chemical substances may be combined or converted to others by means of chemical reactions . </P>
a change in which one or more new substance are formed
a change in which one or more new substance are formed
chemical reactions
chemical reactions