ELEMENTS OF CHEMICAL CHANGE
As a provider of health care, you will not be required in most cases, to write and
balance chemical equations. You will, however, be using and/or seeing the effects of
chemical reactions on a daily basis. Chemical reactions are frequently used to explain
various concepts of pharmacology and physiology. Consider drugs. All drugs are
chemicals and any pharmacological reference you consult will refer to the chemical
changes drugs undergo in the body. Consequently, it is essential that you have a basic
knowledge of what a chemical reaction involves and how that chemical reaction can be
expressed as a chemical equation.
a. Definite Composition. When atoms combine, they do so in definite ratios of
intact atoms to produce compounds with definite composition. Note that this
combination is by number of atoms, not by weights of atoms. What the individual atoms
happen to weigh is not important. Atoms do not know what they weigh. When they do
interact and combine, it is always as whole particles, and the particle-to-particle or
atom-to-atom ratio can always be expressed in simple, whole numbers. Chemical
changes do not split atoms into fractional pieces. This is the reason we are able to write
a formula such as HCl for the compound hydrochloric acid. Hydrochloric acid is always
formed from one atom of hydrogen and one atom of chlorine. Since a chemical reaction
is merely a change in matter, and matter consists of atoms or molecules, we can
discuss chemical reactions by talking about interactions of individual molecules or
b. Chemical Equations. In discussing a chemical reaction, it would be very
cumbersome to write it out in the same manner as we state it verbally. To get around
this problem, chemists have developed chemical equations. Chemical equations are
abbreviated ways of writing chemical reactions. They save much writing and effort and
give at least as much information as a verbally stated reaction. Chemical equations
The kinds of atoms or molecules reacting.
The products formed.
The number of atoms entering the reaction.
The number of molecules formed in the product.
The proportion in which the substances react to give definite products.