What is the chemical changes anyone can observe in the pre-launch, launch and flight of model rocket?
Model rockets are powered by fuel or more accurately propellants, just like any other rocket. There are two types of commonly used fuels- solid and liquid. The propellant consists of fuel and oxidizer, unlike jet engine which draws the oxygen from surroundings. In a solid propellant, the fuel is a hydrocarbon and oxidizer is made up of compound containing oxygen; and both of them are within the chemical. In case of liquid propellant, gases are liquified under pressure and are contained in separate container; to be mixed during rocket flight.
In case of model rockets, the solid propellant is used. The chemical changes that can be observed during pre-launch, launch and flight phases are due to the combustion of this fuel, which causes exhaust of gases. These hot gases power the flight of the rocket and enables it to overcome earth's gravity, by yielding enough thrust. When the fuel is used up, the rocket decelerates and falls back to the ground, assisted by a parachute. Sometimes, the rockets are provided with an ejection charge that causes gases to be generated once the rocket reaches the apogee (highest point in trajectory). This leads to safe and gentle descent of the remaining sections of the rocket.
Hope this helps.