When a piece of copper metal is heated in air,
it comes together with oxygen in the air. Then if it is weighed, it is found
to have a greater mass that the original piece of metal. If however the mass
of the oxygen of the air that combines with the metal is taken into consideration,
it can be shown that the mass of the product is within the limits of accuracy
of any weighing instrument, equal to the sum of the masses of the copper and
oxygen that combine. This behavior of matter is in accord with what is called
the Law of Conservation of Matter: During an ordinary chemical change,
there is no detectable increase or decrease in the quantity of matter.
Conversion of one type of matter into another are always accompanied by the
conversion of one form of energy into another. Usually heat is leveled or
absorbed, but sometimes the conversion involves light or electrical energy
instead of, or in addition to heat. Many transformations of energy, of course,
do not involve chemical changes. Electrical energy can be changed into either
mechanical, light, heat or potential energy without chemical changes. Mechanical
energy is converted into electrical energy in a generator. Potential and kinetic
energy can be converted into one another. Many other conversions are possible,
but all of the energy involved in any change always appears in some form after
the change is completed.
The Law of Conservation of Energy states that energy cannot be created
or destroyed, but can change its form.
The total quantity of matter and energy available in the universe is a
fixed amount and never any more or less.