Propene is an alkene produced by cracking. Describe how propene could be identified using a chemical test, and explain why propene reacts in this way but propane does not. In your answer, refer to the bonding in both molecules.

Add a drop of bromine water to each substance.
1. Propene: the orange colour of the bromine water disappears, becoming colourless.
2. Propane: the orange colour remains unchanged.
Propene is unsaturated, containing a C=C double bond. The π‑electrons are available for electrophilic addition of Br₂, breaking the double bond and forming 1,2‑dibromopropane, which removes the bromine colour. Propane is saturated, with only C–C and C–H single bonds; it has no π‑electrons and therefore cannot undergo electrophilic addition, so bromine water is not consumed.