Reactions and Periodicity
IN THIS CHAPTER
Summary: Chemistry is the world of chemical reactions. Chemical reactions
power our society, our environment, and our bodies. Some chemical species
called reactants are converted into different substances called products.
During this process, there are energy changes that take place. It takes energy to
break old bonds. Energy is released when new bonds are formed. Does it take
more energy to break the bonds than is released in the formation of the new
bonds? If so, energy will have to be constantly supplied to convert the reac-
tants into products. This type of reaction is said to be endothermic, absorbing
energy. If more energy is released than is needed to break the old bonds, then
the reaction is said to be exothermic, releasing energy. The chemical reactions
that provide the energy for our world are exothermic reactions. In Chapter 9,
Thermodynamics, you can read in more depth about the energy changes that
occur during reactions.
Reactions occur because of collisions. One chemical species collides with
another at the right place and transfers enough energy, and a chemical reaction
occurs. Such reactions can be very fast or very slow. In Chapter 14 on Kinetics, you
can study how reactions occur and the factors that affect the speed of reactions.
But in this chapter we will review the balancing of chemical equations, discuss the
general types of chemical reactions, and describe why these reactions occur.Keywords and Equations
There are no keywords or equations listed on the AP exam that are specific to this
chapter.CHAPTER
6KEY IDEA
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