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CONCEPTS Applied

Most for the Money
Chemical fertilizers are added to the soil when it does not
contain sufficient elements essential for plant growth (see
Figure 10.1). The three critical elements are nitrogen,
phosphorus, and potassium, and these are the basic
ingredients in most chemical fertilizers. In general, lawns
require fertilizers high in nitrogen, and gardens require
fertilizers high in phosphorus.
Read the labels on commercial packages of
chemical fertilizers sold in a garden shop. Find the
name of the chemical that supplies each of these critical
elements; for example, nitrogen is sometimes supplied
by ammonium nitrate NH 4 NO 3 . Calculate the mass
percentage of each critical element supplied according
to the label information. Compare these percentages to
the grade number of the fertilizer, for example, 10–20–
10. Determine which fertilizer brand gives you the most
nutrients for the money.
FIGURE 10.4 The charcoal used in a grill is basically carbon.
The carbon reacts with oxygen to yield carbon dioxide. The chemical
equation for this reaction, C + O 2 → CO 2 , contains the same infor-
mation as the English sentence but has quantitative meaning as well.

10.2 CHEMICAL EQUATIONS The arrow means yields, and the word equation is read, “Carbon

Chemical reactions occur when bonds between the outermost reacts with oxygen to yield carbon dioxide.” This word equation
parts of atoms are formed or broken. Bonds are formed, for ex- describes what happens in the reaction but says nothing about
ample, when a green plant uses sunlight—a form of energy— the quantities of reactants or products.
to create molecules of sugar, starch, and plant fibers. Bonds
are broken and energy is released when you digest the sugars
and starches or when plant fibers are burned. Chemical reac-
tions thus involve changes in matter, the creation of new ma- Myths, Mistakes, & Misunderstandings
terials with new properties, and energy exchanges. So far, you
have considered chemical symbols as a concise way to repre- Chemical Reactions to Fool Breathalyzer Test?
sent elements and formulas as a concise way to describe what a Suppose someone consumes too much alcohol and then tries
compound is made of. There is also a concise way to describe a to drive a car. Police notice the erratic driving and stop the
chemical reaction, the chemical equation. driver. Can the driver cause a chemical reaction to quickly
fool the soon-to-be-administered breathalyzer test? Have you
heard, for example, that sucking on a copper penny will cause
BALANCING EQUATIONS a chemical reaction that will fool the breathalyzer, resulting
Word equations are useful in identifying what has happened be- in a low reading? This is a myth, of course, as the breatha-
fore and after a chemical reaction. The substances that existed lyzer measures blood alcohol content by sampling air from the
before a reaction are called reactants, and the substances that subject’s lungs. Even if copper from a penny caused a chemi-
cal reaction in a person’s saliva (which is doubtful), it would
exist after the reaction are called the products. The equation has
not react with or change the amount of alcohol in exhaled air
a general form of
from the lungs. Other variations on this myth that also have
reactants → products no scientific basis include sucking on a nickel; eating cough
drops, garlic, or curry powder; or chewing vitamin C tablets.
where the arrow signifies a separation in time; that is, it identi- The bottom line is there is nothing you can do to change the
fies what existed before the reaction and what exists after the breathalyzer reading—except to not consume alcohol before
reaction. For example, the charcoal used in a barbecue grill driving.
is carbon (Figure 10.4). The carbon reacts with oxygen while
burning, and the reaction (1) releases energy and (2) forms
carbon dioxide. The reactants and products for this reaction
can be described as
Chemical symbols and formulas can be used in the place of
carbon + oxygen → carbon dioxide words in an equation, and the equation will have a whole new

10-5 CHAPTER 10 Chemical Reactions 255