Lesson 9: Classifying Chemical Reactions

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Now for the second half of chapter 7:

Textbook Reading:  For lesson 9, please read Chapter 7, pp. 218 to Key Terms on top of page 238.



A. One way to classify chemical reactions is by what type of chemistry is happening.

1. Precipitation reactions 

These are some of the more memorable reactions in chemistry, particularly because there is a clear sign that a reaction has occurred. Whether or not a precipitate forms has to do with solubility of the products.

Did you understand what spectator ions are?

2Na+(aq) + 2Cl(aq) + Cu2+(aq) + SO42−(aq) →

2Na+(aq) + SO42−(aq) + CuCl2 (s)

Can you find the spectator ions in the equation above? If not, try this tutorial. Can you find the precipitate in this reaction? (Answer posted here)

One of your classmates suggested this beautiful precipitation reaction between potassium iodide and lead (II) nitrate. Enjoy!

2. Acid-Base or Neutralization Reactions

When acids and bases are added together, the end products are often water and a salt (ionic compound).


3. Gas Evolution Reactions

Remember the baking soda and vinegar volcanoes you did as child? Those frothy bubbles were caused by the release of carbon dioxide gas, making it an example of a gas evolution reaction.

4. Oxidation-Reduction or “Redox” Reactions

Although mentioned here, we don’t have all the chemistry knowledge we need to completely understand these reactions. We’ll visit them again in Chapter 16 after we learn more about electrons and bonding.

Combustion is a specific type of oxidation-reduction reaction.

Note: The reaction of octane to form carbon dioxide and water in an internal combustion engine is shown on the bottom of page 227.

2C8H18 + 25O2 ==> 16CO2 + 18H2O

This is the idealized reaction under the best possible conditions. In reality the combustion of gasoline produces CO (carbon monoxide), NO (Nitrogen Oxide), O3 (ozone), etc. These side reactions can result in serious air pollution issues.

B. A second way to classify reactions is to look at what the atoms are doing.

1. Synthesis or combination
2. Decomposition
3. Displacement (or called single replacement)
4. Double-displacement – double-replacement

People have come up with a number of fun ways to remember these reactions, for example:

Classifying Chemical Reactions (with reference to the) Flintstones

Or you might remember this poster involving happy/sad faces.

Hope you found that helpful. Please let me know if you have any questions!

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