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Combination Reactions

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It's Better Together
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It’s Better Together

Credit: Alisha Vargas
Source: http://www.flickr.com/photos/alishav/3792177673/
License: CC BY-NC 3.0

Salt is a common ionic substance that nearly everyone has observed. It forms a nice crystalline solid most people would characterize it as “stable”. Interestingly, it can be synthesized via the combination reaction of two very unstable elements – sodium (a metal) and chlorine (a non-metal). These two elements so desperately want to combine to form the salt sodium chloride that it could be dangerous to your health to get in their way!

Amazing But True!

  • It is always remarkable how two different substances can be combined to form a new substance. Furthermore, the new substance can have physical and chemical properties that are completely different from the starting materials. A great example of this is how the compound sodium chloride is a tasty, white crystalline solid that is made from sodium (a soft, conducting and flammable solid metal) and chlorine (a yellow-green toxic gas).
  • Credit: Sandor Iskender
    Source: http://www.flickr.com/photos/iskender/422532661/
    License: CC BY-NC 3.0

    Sodium can also be used for streetlights [Figure2]

     

  • Watch the formation of salt via the combination reaction of sodium and chlorine:

https://www.youtube.com/watch?v=2mzDwgyk6QM

Can You Apply It?

With the links below, learn more about combination reactions to produce ionic compounds from elemental starting materials. Then answer the following questions.

  1. Combination reactions can be used to prepare a variety of stable ionic compounds. If you know what the most stable ions of various elements are you can predict the formulae for these ionic compounds. What are the stable ionic compounds that come from the combination reaction of: i. Potassium and Oxygen; ii. Lithium and Fluorine; iii. Calcium and Nitrogen?
  2. For reactions to occur “naturally” (this is called spontaneity in chemistry) they either need to give off energy or lead to more disorder (or possibly both of these). Combination reactions generally lead to more order (since they lead to previously “free” starting materials to be “bound” to each other). What can you predict about the flow of energy in combination reactions?

Image Attributions

  1. [1]^ Credit: Alisha Vargas; Source: http://www.flickr.com/photos/alishav/3792177673/; License: CC BY-NC 3.0
  2. [2]^ Credit: Sandor Iskender; Source: http://www.flickr.com/photos/iskender/422532661/; License: CC BY-NC 3.0

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