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Elementary Science Education

The Rules for Reading/Writing Chemical Equations

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      Bernard Nebel

      For this lesson and beyond, kids will need to know how to read/interpret chemical formulas for compounds and reactions. It may seem like Greek at first, but once the rules are understood it is really quite easy. 

      Consider the chemical equation for the oxidation/burning of the sugar, glucose.

      C6H12O6   +  6O2    —->     6CO2    +      6H2O   +  energy

      Glucose       oxygen      carbon dioxide    water      energy

      This formula says that a single molecule (the smallest basic unit) of glucose is constructed from six atoms of carbon, twelve atoms of hydrogen, and six atoms of oxygen. Note how subscripts following the element specify the number of atoms of that element in the molecule.

      The + can be reads as “mixed with”.

      Six molecules of oxygen gas, each consisting of two oxygen atoms boded together; Note that the number of in front of a formula specifies the number of that molecule. If no number is present it is assumed to be one. 

      —> The arrow says reacts with to produce…

      As above, you can interpret the formulas for carbon dioxide and water.

      The compounds that go into a reaction and called the reactants; those that are produces and called the products.

      A very important aspect of a chemical equations for a reaction harks back to a basic grade-one lesson. Matter is neither created or destroyed. Therefore, the same number of atoms of each element must be represented on both sides of the arrow. If this were not the case, we would be indicating the creation or destruction of one or more atoms. This simply does not occur in chemical reactions. 

      Last point: The chemical equation represents the “lowest common denominator”, the minimum number of molecules. However, this shows the ratio of reactants and products and this ratio remains constant regardless of actual quantities involved. In this case the equation says: 6 molecules of oxygen will be consumed for every one molecule of glucose oxidized, and 6 molecules of carbon dioxide and 6 molecules of water will be produced. 

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