Chemical reaction- transformation of one or more substance into different substances. Combustion reaction- reaction in which a substance reacts with oxygen (from air), emitting heat and forming one or more oxygen containing compounds. Evidence of a chemical change can be one of the following: Emission of light/ emission or absorption of heat. When water boils, bubbles for and a gas is evolved, but no chemical reaction has occurred: they are both composed of the same thing: water molecules, no change in chemical composition. Boiling point and melting point and phase changes. Y or n: butane burning in a butane lighter- yes combustion reaction, butane evaporating out of a butane lighter- n physical change, wood burning- yes combustion reaction, dry ice (solid co2) subliming- no physical change. We represent a chemical reaction with chemical equation: Reactants: shown to the left of the arrow. Products: shown to the right of the arrow. The state is stated next the each reaction and product!