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Video:How to Balance Chemical Equations

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The key to balancing chemical equations is remembering that you need to end up with the same number of atoms that you start with. This video will give you a brief tutorial on balancing chemical equations.See Transcript

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Transcript:How to Balance Chemical Equations

Hi, today we're going to learn how to balance a chemical equation.

Unbalanced Chemical Equation

Al + CuSO4 → Al2(SO4)3 + 3Cu

On the left hand side of a chemical equation we write our reactants, or the chemicals that we start with. In this case, we are starting out with copper II sulfate and aluminum. It's important to note the state of matter for our substances. In this example, we need to write a subscript (s) next to the aluminum to denote a solid, and an (aq) next to the copper II sulfate, since it's dissolved in water.

On the right hand side of the equation, we write down our products, or what we'll have after the reaction is over. In this reaction, the aluminum will displace the copper ion and kick it out of the solution to form copper metal.

Al (s) + CuSO4 (aq) → Al2(SO4)3 (aq) + Cu (s)

Identifying Number of Atoms in Equation

The skeleton of our reaction is there, but the equation is not yet balanced. We have 1 aluminum on the left side of the equation and 2 on the right; and 1 sulfate on the left and 3 on the right. But the conservation of mass law states that we need to end up with the same amount of atoms that we started with.

Begin by Balancing Compounds

It is easier to balance the lone atoms, so we'll save those for last, and start with balancing the sulfate ion. The sulfate is featured on both sides of the equation, so we can treat it as a single unit, rather than break up into the individual atoms. Because we have three sulfates on the right side, the left side of the equation also needs to have three. So we'll put 3 in front of the entire compound "copper II sulfate". Note we can't put the 3 as a subscript, because that would completely change the chemical formula, and we wouldn't have copper II sulfate any longer.

Al (s) + 3CuSO4 (aq) → Al2(SO4)3 (aq) + Cu (s)

Balance Lone Atoms in Equation

Because a 3 is now in front of the copper II sulfate, we now have 3 molecules of this substance. Where there was 1 copper atom, we now have 3. On the right, however, we still have only 1 copper. So we'll need to put a large 3 in front of the copper metal here.

Al (s) + 3CuSO4 (aq) → Al2(SO4)3 (aq) + 3Cu (s)

Now both the copper and the sulfate are balanced, but we're not done yet! We still have to balance the aluminum. Since the right hand side has 2 aluminums, we need to also have 2 aluminums on the left, so we'll write a large 2 in front of the aluminum.

2Al (s) + 3CuSO4 (aq) → Al2(SO4)3 (aq) + Cu (s)

And this is how you balance a chemical equation. For more information, please visit us at About.com.

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