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Recognizing Chemical Reactions

Visual clues that indicate a chemical reaction is occurring.

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A Delicious Reaction

A Delicious Reaction

Credit: US Navy
Source: http://commons.wikimedia.org/wiki/File:US_Navy_090818-N-6326B-001_Staff_and_patients_participate_in_a_healthy_cooking_class_at_Naval_Medical_Center_San_Diego.jpg
License: CC BY-NC 3.0

Many synthetic chemists call the act of making new molecules “cooking.”  How appropriate!  When you cook food, a whole array of chemical reactions are occurring.

News You Can Use

  • Chemical reactions are all around us.  Cooking food is one category that affects all of us everyday.  For example, carbon dioxide is produced by yeast in bread, allowing the dough to rise.  When the dough is placed in an oven, the heat causes chemical reactions to occur.  
  • Credit: Moyan Brenn
    Source: http://www.flickr.com/photos/aigle_dore/5951666351/
    License: CC BY-NC 3.0

    The holes in the bread are caused by air bubbles produced by the yeast [Figure2]


  • In the kitchen, ingredients lead to finished dishes; however, in the lab, reactants lead to isolated products.  Chemical reactions always lead to chemical changes – the creation of new chemical compounds!
  • Watch a compilation of some exciting reactions: http://www.youtube.com/watch?v=UkBhW8Kj3r8

Show What You Know

With the links below, learn more about recognizing chemical reactions. Then answer the following questions.

  1. List and describe in detail three ways you know a chemical reaction has occurred.
  2. A change in melting point is sometimes identified as evidence of a chemical reaction.  Can the same be said of a change in freezing point?
  3. Why might plunging a vegetable into boiling water cause it to become bright green in color?
  4. Consider your answers for question 1 above.  Which of the observations are related to energy transfer in the chemical reaction and which are related to the formation of new products?

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