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Chemical reactions are the heart of chemistry. Some reactions, such as those
accompanying a forest fire or the explosion of dynamite, are quite dramatic.
Others are much less obvious, although all chemical reactions must involve
detectable change. A chemical reaction involves a change from reactant substances
to product substances, and the product substances will have physical and chemical properties different from those of the reactants.
Figure 4.1 shows an experimenter adding a colorless solution of potassium
iodide, KI, to a colorless solution of lead(II) nitrate, Pb(NO3)
. What you see is the formation of a cloud of bright yellow crystals where the two solutions have come into
contact, clear evidence of a chemical reaction. The bright yellow crystals are lead(II)
iodide, PbI2
, one of the reaction products. We call a solid that forms during a chemical reaction in solution a precipitate; the reaction is a precipitation reaction.
In this chapter, we will discuss the major types of chemical reactions, including
precipitation reactions. Some of the most important reactions we will describe involve
ions in aqueous (water) solution.Therefore, we will first look at these ions and see how
we represent by chemical equations the reactions involving ions in aqueous solution.
Some questions we will answer are: What is the evidence for ions in solution?
How do we write chemical equations for reactions involving ions? How can we classify and describe the many reactions we observe so that we can begin to understand
them? What is the quantitative description of solutions and reactions in solution?
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