Balancing Chemical Equations

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Have you ever used a recipe to prepare food? If not, most likely you have at least seen a recipe and have an idea how they are to be used. A recipe is a set of instructions that will be used to combine ingredients in order to prepare or make something. Most often we see recipes used in cooking, however, lets look at even simpler example.

bicycleImagine you had a job assembling bicycles. In order to correctly assemble the bicycles, you used a set of instructions (a “recipe” of sorts). This recipe was simple: 1 bike frame, 2 wheels and you have a bicycle!

Let’s try and use this simple recipe to make some calculations. If your boss asked you to build 2 bicycles, how many many wheels and how many bike frames would you need? Well, since we have doubled end result of our recipe we need to also double all of our “ingredients.” Therefore, I would need 2 bike frames and 4 wheels. Let’s try another one. What if you had 8 wheels, how many bicycles could you make and how many bike frame would you require? Since the recipe calls for 2 wheels and I have 8 wheels, I have multiplied the number of wheels in my recipe by 4. Since I multiplied the number of wheels in the recipe by 4, I must do the same for each of the other parts of the recipe. Therefore, I can make 4 bicycles and I would need 4 bike frames to use all of my wheels.

Just as we were able to predict the number of bicycles we could make by using our “bicycle recipe,” we can predict the amount of a substance we can produce through a chemical reaction. A chemical reaction is the process of changing a substance (or substances) into one or more new substances. In order to predict the amount of new substance we can produce, we must start with a recipe. The recipe we use for a chemical reaction is a called a chemical equation. Here’s and example of a chemical equation:

chemical equation

Figure 1

In this chemical equation we call hydrogen and oxygen the reactants and we call water the product. Thus, all chemical equations take on the form:

word equation

Figure 2

 

You may have noticed that there is a slight problem with our chemical equation in figure 1. On the reactant side of the equation there are 2 oxygens however, on the product side there is only 1 oxygen. What happened to the other oxygen!? The Law of Conservation of Mass tells us that matter cannot be created or destroyed so we must fix our chemical equation. Our chemical equation in figure 1 is called a skeleton equation. A skeleton equation only describes the identity of the reactants and the products, it does not describe the relative amounts of reactants and products. For our chemical equation to be useful, we must turn our skeleton equation into a balanced chemical equation. A balanced chemical equation has the same number of atoms on each side of the equation. To balance our chemical equation we can use coefficients (small whole numbers that are placed in front of the chemical formulae in our chemical equation) to act as multipliers and increase the amount of our products and reactants until they are balanced on both sides.

 

Here is our skeleton chemical equation:

chemical equation

Figure 1

 

Since we are missing an oxygen on the product side, we can place the coefficient, 2, in front of the water molecule.

half balanced

Figure 3

 

Now we can see that the oxygen is balanced on both sides, however, the hydrogen is no longer balanced. On the product side there are 4 hydrogens and on the product side there are only 2 hydrogens on the reactant side. To remedy this, we can place the coefficient, 2, in front of the Hydrogen on the reactant side.

Balanced

Figure 4

 

Now we have a balanced chemical equation!

 

 

You can be successful in balancing any chemical equation as long as you follow these steps:

  1. Start by balancing the metals in the equation
  2. After the metals are balanced, balance the nonmetals in the equation
  3. Leave hydrogen and oxygen until the end, usually they will balance themselves!

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