prhedching wheather

The chemical reactions that are most important to us occur in water—
in aqueous solutions. Virtually all of the chemical reactions that keep
each of us alive and well take place in the aqueous medium present in our
bodies. For example, the oxygen you breathe dissolves in your blood,
where it associates with the hemoglobin in the red blood cells. While attached
to the hemoglobin it is transported to your cells, where it reacts
with fuel (from the food you eat) to provide energy for living. However,
the reaction between oxygen and fuel is not direct—the cells are not tiny
furnaces. Instead, electrons are transferred from the fuel to a series of
molecules that pass them along (this is called the respiratory chain) until
they eventually reach oxygen. Many other reactions are also crucial to our
health and well-being. You will see numerous examples of these as you
continue your study of chemistry.
In this chapter we will study some common types of reactions that
take place in water, and we will become familiar with some of the driving
forces that make these reactions occur. We will also learn how to predict
the products for these reactions and how to write various equations to describe
them.
Predicting Whether a Reaction Will Occur
To learn about some of the factors that cause reactions to occur.
In this text we have already seen many chemical reactions. Now let’s consider
an important question: Why does a chemical reaction occur? What
causes reactants to “want” to form products? As chemists have studied reactions,
they have recognized several “tendencies” in reactants that drive them
to form products. That is, there are several “driving forces” that pull reactants
toward products—changes that tend to make reactions go in the direction
of the arrow. The most common of these driving forces are
1. Formation of a solid
2. Formation of water
3. Transfer of electrons
4. Formation of a gas
When two or more chemicals are brought together, if any of these
things can occur, a chemical change (a reaction) is likely to take place. Accordingly,
when we are confronted with a set of reactants and want to predict
whether a reaction will occur and what products might form, we will
consider these driving forces. They will help us organize our thoughts as we
encounter new reactions.
Reactions in Which a Solid Forms
To learn to identify the solid that forms in a precipitation reaction.
One driving force for a chemical reaction is the formation of a solid, a
process called precipitation. The solid that forms is called a precipitate,
and the reaction is known as a precipitation reaction. For example,
7.2 Reactions in Which a Solid Forms 167
OBJECTIVE:
7.1
OBJECTIVE:
7.2
Royalty-Free Corbis
Sign in to OWL at
www.cengage.com/owl to view
tutorials and simulations, develop
problem-solving skills, and complete
online homework assigned by your
professor.
Download mini-lecture videos
for key concept review and exam prep
from OWL or purchase them from
www.ichapters.com
A burning match involves several
chemical reactions.