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Classifying Chemical Reactions

Objectives:

    1.    Name 4 general types of chemical reactions.

    2.    Describe each of the four types of chemical reactions.

Key Terms:

    direct combination reaction    decomposition reaction    single-replacement reaction    double-replacement reaction

Notes: (9-3)

Most chemical reactions can be broken down into four simple types of reactions.  Knowing the type of reaction helps us predict the product of the reactants.

Direct combination reaction:

All reactants combine into the product.    A + B g AB
Also called a synthesis reaction
No matter how many reactants are present there is only one product

Example:    C + CO2 g 2CO    or    Na + Cl g NaCl

Decomposition reaction:

A single reactant breaks down into multiple products.    AB g A + B
Is the reverse of the direct combination reaction.

Example:    2H2O g 2H2 + O2

Single-replacement reaction:

The reactants and products both consist of an element and a compound.        AB + C g AC + B
Generally occurs in ionic compounds
Most occur as a result of being dissolved in water
Replacement is based on the chemical activity of the metals.

Example:    Fe + CuSO4 g Cu + FeSO4

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Double-replacement reaction:

Atoms and ions from 2 different compounds replace each other.     AB + CD g AC + BD
Most occur as a result of being dissolved in water
Indicators that a double replacement reaction has taken place:
    precipitation - solid separates in solution
    effervescence - gas bubbles form 
    at least one of the products is a molecular compound
 

 

Last modified: December 11, 2002