A physical change changes state, shape or arrangement without producing a new substance. A chemical change forms new substances with different properties. Use evidence chains rather than “one clue proves it”.
Possible reaction indicators include formation of a new gas, a new solid precipitate, a persistent colour or property change, and a temperature change. Bubbles alone do not prove reaction because boiling is physical; colour alone can change because of mixing or indicators.
In an exothermic reaction, energy is transferred from the reacting system to the surroundings and measured temperature often rises. In an endothermic reaction, the system absorbs energy from surroundings and measured temperature often falls. Applied testing kits—such as soil, water or diagnostic colour tests—use chemical indicators, but every test has limits and needs interpretation.