What is the first law of thermodynamics and how does it apply to chemistry?
The first law of thermodynamics is that mass energy is always conserved in a closed system (yes, such as the universe). Mass energy is always equal in any chemical or nuclear reaction.
In all chemical and nuclear reactions the amount of energy in the reactants must always equal the amount of energy in the products, in a closed reaction vessel.
The energy may be changed from potential to heat or kinetic in most spontaneous reactions. In some reactions kinetic energy or order is changed to potential energy.
In nuclear energy mass can be changed into energy but the total of mass and energy must always remain the same. Matter and Energy can not be either created or destroyed by any known natural laws or processes, in a closed system.