the law of conversation of (mass/energy) states that the total mass before a chemical reaction is the same as the totally mass after the reaction. which is one is it mass or energy?

The law of conservation of mass says that matter cannot be created or destroyed by ordinary chemical or physical changes.

This means:

The mass will be the same before and after the chemical or physical change

There are the same number of each type of atom before and after the change

The total mass of all components of a chemical reaction or physical change can be measured before and after the change to demonstrate that the mass is constant.

Scientists believe that energy is conserved, like mass, during a physical or chemical change. The law of conservation of energy says that energy can be converted from one form to another, but it cannot be created or destroyed in ordinary chemical or physical changes.

Energy can be more challenging for scientists to keep track of during a chemical reaction than mass. Mass is able to be measured on a balance before and after the change, but scientists must use more advanced techniques to measure the energy in a system.

Energy is converted from one form to another during a chemical change. This energy is not created or destroyed; it is just converted from one form of energy to another during the chemical and physical changes that occur.

Physical Change: In a physical change, atoms are rearranged but remain in the same sample of matter. The same numbers of atoms are present before and after the change, and they have the same total mass. Atoms are spread farther apart or pushed closer together during a phase change. When a substance changes phases, the volume may change but the mass doesn't.

Chemical Change: In a chemical change, the original bonds are broken and new bonds are formed. The same atoms are present before and after a chemical change, they are just rearranged to make different compounds.