WHAT IS A CHEMICAL REACTION?
A chemical reaction is material changing from a beginning mass to a resulting
substance. The hallmark of a chemical reaction is that new material or materials are
made, along with the disappearance of the mass that changed to make the new.
This does not mean that new elements have been made. In order to make new
elements, the nuclear contents must change. There are magnitudes of difference in the
amounts of energy in ordinary chemical reactions compared to nuclear reactions. The
energy of rearrangement of the nuclei of atoms to change to new elements is
enormous compared to the smaller energies of chemical changes. The alchemists, in
their efforts to change less expensive metals to gold, did not have the fundamental
understanding of what they were attempting to do to appreciate the difference.
A chemical equation is a way to describe what goes on in a chemical reaction, the
actual change in a material. Chemical equations are written with the symbols of
materials to include elements, ionic or covalent compounds, aqueous solutions, ions,
or particles. There is an arrow pointing to the right that indicates the action of the
reaction. The materials to the left of the arrow are the reactants, or materials that are
going to react. The materials to the right of the arrow are theproducts, or materials
that have been produced by the reaction. The Law of Conservation of Mass states that
in a chemical reaction no mass is lost or gained. The Law of Conservation of Mass
applies to individual types of atom. One could say that for any element, there is no
loss or gain of that element in a chemical reaction. There are such things as reversible
reactions, reactions in which the products reassemble to become the original products.
Reversible reactions are symbolized in chemical equations by a double-headed arrow,
but the standard remains to call the materials on the left the reactants and the materials
on the right the products.
A chemical reaction is a process that leads to the transformation of one set of chemical substances to
another.[1] Chemical reactions can be either spontaneous, requiring no input of energy, or non-
spontaneous, often coming about only after the input of some type of energy, viz. heat, light or electricity.
Classically, chemical reactions encompass changes that strictly involve the motion of electrons in the
forming and breaking of chemical bonds, although the general concept of a chemical reaction, in
particular the notion of a chemical equation, is applicable to transformations of elementary particles, as
well as nuclear reactions.
The substance/substances initially involved in a chemical reaction are called reactants. Chemical
reactions are usually characterized by a chemical change, and they yield one or more products, which
usually have properties different from the reactants.
Different chemical reactions are used in combination in chemical synthesis in order to get a desired
product. In biochemistry, series of chemical reactions catalyzed by enzymes form metabolic pathways, by
which syntheses and decompositions impossible under ordinary conditions are performed within a cell.
What Is a Chemical Reaction?
If liquid water is boiled, it is still water; likewise frozen water, or ice, is still water. Melting, boiling, or
freezing simply by the application of a change in temperature are examples of physical changes,
because they do not affect the internal composition of the item or items involved. A chemical change,
on the other hand, occurs when the actual composition changes—that is, when one substance is
transformed into another. Water can be chemically changed, for instance, when an electric current is
run through a sample, separating it into oxygen and hydrogen gas.
Chemical change requires a chemical reaction, a process whereby the chemical properties of a
substance are altered by a rearrangement of the atoms in the substance. Of course we cannot see
atoms with the naked eye, but fortunately, there are a number of clues that tell us when a chemical
reaction has occurred. In many chemical reactions, for instance, the substance may experience a
change of state or phase—as for instance when liquid water turns into gaseous oxygen and hydrogen
as a result of electrolysis.
B, Paraffin wax melts into a liquid state when heated, but hardens again when cooled.
