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Common Reactions

Photosynthesis reactions are naturally occurring processes that take place in all green plants and most algae. During this process the plant uses light energy, carbon dioxide, and water to make food and then releases oxygen which many living organisms require to the atmosphere.

Photosynthesis is a series of complicated chemical reactions that mankind has not been able to reproduce. Most reactions take place during daylight hours while some occur during the night.

In 7th Grade Integrated Science you learned that plant cells contain chloroplasts, which are organelles found only in the plants. These organelles contain the green pigment chlorophyll. There may also be other pigments in plants that are more easily seen in the fall. The photosynthesis reactions occur in the colored pigments in plant cells. During the photosynthesis process, plants capture light energy and use that energy to make glucose. Another product of this reaction is oxygen, which is released as a gas. Here is the chemical equation for photosynthesis:

There is a reaction that is the opposite of photosynthesis called respiration.

From the knowledge you have gained, what do you think the reactants and products in the respiration reaction would be?

The equation for respiration is:

This equation can be read as "Glucose combines with six oxygen to yield six carbon dioxide plus six water." This process - the reverse of photosynthesis is known as respiration. Animals like us need energy which is obtained from sugars. Respiration occurs in the mitochondria of cells. During respiration, sugar is broken down in a chemical reaction with oxygen. The end products of the respiration reaction are the smaller compounds of carbon dioxide and water. (Notice the products and reactants of respiration and photosynthesis are exact opposites.)

Respiration is almost the exact opposite reaction to photosynthesis. These two reactions work together to maintain a biological energy balance on earth.


Another common reaction is combustion. In a combustion reaction, for example a Jet Ski burning gasoline to produce energy, oxygen combines with gasoline and produces carbon dioxide and water. The reaction may be written as:
Anytime something burns it is a combustion reaction.
Everyone has seen something rust. Remember when we talked about rusting or oxidation. This is another common reaction. Iron rusting may be written as:


  1. Cite four examples of common chemical reactions.
  2. Look at the picture of the statue of liberty. She is made of copper like a new penny (put your mouse over the picture to see how she used to look). Why is she green?
  3. The way we use our natural resources sets us apart from less technological societies. Which of these reactions powers our society?
  4. Fuel cells produce energy by burning Hydrogen and Oxygen to produce water. The equation is: 2H2 + O2 ? 2H20. What advantages do you see by replacing the use of fossil fuels with fuel cells?

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Updated October 24, 2008 by: Glen Westbroek

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