Chemical Reactions
A chemical reaction is a process that leads to the conversion of one type of chemical substances to another. Chemical reactions can be either spontaneous which means requiring no contribution of energy, or non-spontaneous which means typically following the input of some kind of energy, like heat, electricity or light. Typically, chemical reactions include changes that strictly include the motion of electrons in forming and breaking of chemical bonds among atoms, and can sometimes be explained by a chemical equation.
The common concept of chemical reactions between atoms has been expanded to the non-chemical reactions among entities smaller than atoms, involving radioactive decays, nuclear reactions, and reactions between elementary particles as explained by quantum field theory.