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Balancing Chemical Equations

How to Balance a Chemical Equation

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A balanced chemical equation describes the quantities and identities of reactants and products.

A balanced chemical equation describes the quantities and identities of reactants and products.

Don Farrall, Getty Images

Being able to balance chemical equations is a vital skill for chemistry. Here's a look at the steps involved in balancing equations, plus a worked example of how to balance an equation.

Steps of Balancing a Chemical Equation

  1. Identify each element found in the equation. The number of atoms of each type of atom must be the same on each side of the equation once it has been balanced.
     
  2. What is the net charge on each side of the equation? The net charge must be the same on each side of the equation once it has been balanced.
     
  3. If possible, start with an element found in one compound on each side of the equation. Change the coefficients (the numbers in front of the compound or molecule) so that the number of atoms of the element is the same on each side of the equation. Remember! To balance an equation, you change the coefficients, not the subscripts in the formulas.
     
  4. Once you have balanced one element, do the same thing with another element. Proceed until all elements have been balanced. It's easiest to leave elements found in pure form for last.
     
  5. Check your work to make certain the charge on both sides of the equation is also balanced.

Example of Balancing a Chemical Equation

? CH4 + ? O2 → ? CO2 + ? H2O

Identify the elements in the equation: C, H, O
Identify the net charge: no net charge, which makes this one easy!

  1. H is found in CH4 and H2O, so it's a good starting element.
     
  2. You have 4 H in CH4 yet only 2 H in H2O, so you need to double the coeffient of H2O to balance H.

    1 CH4 + ? O2 → ? CO2 + 2 H2O

  3. Looking at carbon, you can see that CH4 and CO2 must have the same coefficient.

    1 CH4 + ? O2 → 1 CO2 + 2 H2O

  4. Finally, determine the O coefficient. You can see you need to double the O2 coefficient in order to get 4 O seen on the product side of the reaction.

    1 CH4 + 2 O2 → 1 CO2 + 2 H2O

  5. Check your work. It's standard to drop a coefficient of 1, so the final balanced equation would be written:

    CH4 + 2 O2 → CO2 + 2 H2O

Take a quiz to see if you understand how to balance equations.

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