Who says chemistry needs to be complicated?
Reactions can be very basic, in fact cooking an egg is an example of a chemical reaction, these reactions are seen as non-reversible. The properties at an atomic level have changed and thus meaning that it cannot change back into the structures the atoms had previously. Another good example would be a firework, the rapid oxidation is an example of a chemical change.
Then there is the example of a physical change, this is an example of where something can be reversed. A good common example that I use in my classes is the changing of water into ice and vice versa. The structure of H20 molecules are kept the same (untouched) and thus can easily change states.
There are two types of reactions:
Chemical reactions - irreversible, for example fireworks or frying an egg
Physical Changes- Reversible, for example Melting ice.