This law relates primarily to chemistry equations, stating that the mass of the reactants and products in simple chemical reactions remains conserved. This law does have limits to its application.
Properly speaking, it is the "Law of Conservation of Energy and Mass". Matter and energy are interchangeable by the relation E=mc^2 . The sum of matter and energy remain constant. If matter is created, an equivalent quantity of energy is consumed. If matter is destroyed, an equivalent quantity of energy is released.
For example: The destruction of an electron releases at least 8.187x10^-14 Joules of energy (note: this does not take into account any linear or angular momentum the electron may have).
Energy=(mass of electron) x (speed of light)^2
Energy=(9.109x10^-31 kg) x (2.998x10^8 m/s)^2
Energy=8.187x10^-14 Joules
For example: The destruction of an electron releases at least 8.187x10^-14 Joules of energy (note: this does not take into account any linear or angular momentum the electron may have).
Energy=(mass of electron) x (speed of light)^2
Energy=(9.109x10^-31 kg) x (2.998x10^8 m/s)^2
Energy=8.187x10^-14 Joules