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Anthony Phys/Chem A & B: Unit 3 Handout
Name: ______________________________
Date: _______________________________
Phys/Chem A & B: Unit 3: Matter and Change
Vocabulary in this section includes~
Decomposition Reaction:
Double-Displacement Reaction:
Neutralization:
Salt:
Single Replacement Reaction:
Synthesis Reaction:
Aqueous:
Solid:
Types of Chemical Reactions:
Why do sodas fizz when you first open them? And why does rust form on metal that is left
outside? Both of these phenomena occur because of chemical reactions, but the way in which the
reactions occur is different. There are actually several different types of chemical reactions.
Reactants may combine, split apart, or replace other reactants to form the final products. In this
lesson, you will learn to recognize five basic types of chemical reactions. Knowing how a given
reaction works will help you understand what is happening and how specific products are being
formed. Chemical reactions go on around and in us all the time. In order to study and understand
them better, scientists have found it helpful to classify the reactions.
Synthesis Reactions:
The first type of reaction you will look at in this lesson is the synthesis reaction. In this type of
reaction, two or more substances combine to form another substance. A and B stand for
appropriate chemicals on the periodic table. For example, they could stand for the reaction in which
iron and oxygen combine to form a new substance, iron III oxide, or rust: They typically follow a
pattern like this one shown here:
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Anthony Phys/Chem A & B: Unit 3 Handout
Synthesis Reactions Continued:
Another example of a synthesis reaction is the combination of hydrogen gas and oxygen gas to form
water:
Decomposition Reactions:
A decomposition reaction is one in which one substance breaks down into two or more new
substances. Reactions of this type are extremely important during the process of digestion.
Complex proteins in the food we eat are broken down into smaller proteins, peptides, or amino
acids. These units are then transported to cells where they will be used as raw materials for new
proteins. These reactions follow a process exactly the opposite of synthesis reactions:
A decomposition reaction you know well is bread dough that rises before it is baked. You probably
know that yeast causes the bread to rise, but have you ever wondered why that happens? Yeast
provides the enzymes that allow simple sugars to decompose into ethanol and carbon dioxide gas.
The release of the carbon dioxide gas from the sugar causes the bread to rise. The equation for this
reaction is written as follows:
Decomposition Reaction Continued: Have you ever used hydrogen peroxide as an antiseptic
cleanser on a cut or wound? The decomposition of hydrogen peroxide produces large amounts of
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Anthony Phys/Chem A & B: Unit 3 Handout
oxygen gas that are toxic to bacteria. This makes the compound useful as an antiseptic. The reaction
is written as follows:
Single Replacement Reactions:
Another type of chemical process is the single replacement reaction. In these types of reactions,
one element replaces another element in a compound. Typically, a metal will replace another
metal, or a nonmetal will replace another nonmetal. This is the type of reaction that occurs in a car
battery. Single replacement reactions generally take the following format:
Notice that element A has pushed element B out of the compound BX. On the product side, element
B is now in its pure form and element A is bonded to X forming the compound AX. This can only
happen if A is a more active metal than B. In general, metals from families 1 and 2 will push
transition metals out of compounds. For example, a reaction between iron and a solution of copper
sulfate will form a solid copper precipitate and the compound iron sulfate, which will stay dissolved
in the solution:
**Note: The (aq) written beside the copper sulfate reactant and the iron sulfate product is an
abbreviation for the word aqueous. It simply means these compounds are dissolved. The (s)
written beside the iron reactant and the copper product indicates that they are present as solids.
As the copper is produced, it forms as a solid and will precipitate out of the solution.
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Anthony Phys/Chem A & B: Unit 3 Handout
Double Displacement Reactions:
Reminder: Recall that when an ionic compound dissolves, the compound breaks apart into ions,
which are the actual dissolved particles. Double displacement reactions normally take place
between two ionic compounds. Each compound is dissolved in water or some other solvent. If for
some reason the two solutions are combined, the dissolved particles from the solutions may react
to form a new product. The positive ions of the two dissolved compounds switch places, creating
two new compounds. When this reaction takes place, at least one of the products must be a
precipitate or a gas. The general format for double displacement reactions is as follows:
An example of this type of reaction is the addition of a solution of potassium iodide to a lead nitrate
solution:
Study this equation carefully. Note how the metals (lead - Pb, and potassium - K) have displaced
each other. Because two elements have been displaced, this reaction is called a double
displacement. The ions of lead nitrate are soluble in water. The ions of the other solution,
potassium iodide, are also soluble in water. However, when these two solutions are mixed, the lead
ions and the iodine ions are attracted to each other and form an ionic bond. When this bond forms,
the compound lead iodide is made. Lead iodide is a solid precipitate, which will sink to the bottom
of the beaker.
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Anthony Phys/Chem A & B: Unit 3 Handout
Neutralization Reactions:
A unique class of double displacement reactions specifies that one of the reactants must be an acid
and another base. When an acid and a base of approximately equal strength are combined, the
products will be water and a salt:
A salt is any chemical compound that forms when the negative ions from an acid combine with the
positive ions of a base. The following figure shows several salts and their uses in everyday living.
You may be familiar with the use of antacids to soothe a "sour stomach." An antacid contains a base
called bicarbonate of soda that reacts with stomach acid (mostly hydrochloric acid) to neutralize
the contents.
The reason an acid-base reaction is called a neutralization reaction has to do with the concept of
pH (Remember: pH means percent Hydrogen). Recall that an acid has a low pH (below 7) and a
base has a high pH (above 7). If an acid and a base of approximately the same strength are
combined, the pH level will be brought toward the neutral mark of 7. This is because the hydronium
(H3O+), which is making one solution acidic, reacts with the hydroxide (OH-), which is making the
other solution basic, to produce water:
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Anthony Phys/Chem A & B: Unit 3 Handout
A good example of an acid reacting with a base is the reaction of sodium hydroxide with
hydrochloric acid to produce sodium chloride (table salt) and water:
Review:
In this lesson, you have learned that there are many ways in which chemicals react to form new
products. By looking at the type of reaction, you can better understand how it occurred and why
specific products were formed. There are five main types of chemical reactions:

synthesis reaction

decomposition reaction

single replacement reaction

double displacement reaction

neutralization reaction