HiSET Science: Conservation of Energy and Matter

Law of Conservation of Energy
The law of conservation of energy states that in a closed system, energy cannot be created or destroyed but only changed from one form to another. This is also known as the first law of thermodynamics. Another way to state this is that the total energy in an isolated system is constant.
Energy comes in many forms that may be transformed from one kind to another, but in a closed system, the total amount of energy is conserved or remains constant. For example, potential energy can be converted to kinetic energy, thermal energy, radiant energy, or mechanical energy. In an isolated chemical reaction, there can be no energy created or destroyed. The energy simply changes forms.

Law of Conservation of Mass
The law of conservation of mass is also known as the law of conservation of matter. This basically means that in a closed system, the total mass of the products must equal the total mass of the reactants. This could also be stated that in a closed system, mass never changes. A consequence of this law is that matter is never created or destroyed during a typical chemical reaction. The atoms of the reactants are simply rearranged to form the products. The number and type of each specific atom involved in the reactants is identical to the number and type of atoms in the products. This is the key principle used when balancing chemical equations. In a balanced chemical equation, the number of moles of each element on the reactant side equals the number of moles of each element on the product side.

Conversion of Energy Within Chemical Systems
Chemical energy is the energy stored in molecules in the bonds between the atoms of those molecules and the energy associated with the intermolecular forces. This stored potential energy may be converted into kinetic energy and then into heat. During a chemical reaction, atoms may be rearranged and chemical bonds may be formed or broken accompanied by a corresponding absorption or release of energy, usually in the form of heat. According to the first law of thermodynamics, during these energy conversions, the total amount of energy must be conserved.