A chemical equation is a theoretical or written representation of what happens when a chemical reaction takes place. The law of conservation of mass states that no atoms can be created or destroyed in a chemical reaction, so the number of atoms in the reactants must balance the number of atoms in the products. Follow this guide to learn how to balance chemical equations.
Step
Step 1. Write down the equation given to you
For this example, you would use:
C3H8 + O2 H2O + CO2
Step 2. Write down the number of atoms you have on each side of the equation
Look at the index below next to each atom to find the number of atoms in the equation.
- Left side: 3 carbons, 8 hydrogens, and 2 oxygens.
- Right side: 1 carbon, 2 hydrogen, and 3 oxygen.
Step 3. Always leave the hydrogen and oxygen until the end of the calculation
This means you need to balance the carbon atoms first.
Step 4. Add a coefficient on the single carbon atom on the right side of the equation to balance with the 3 carbon atoms on the left side
C3H8 + O2 H2O + 3CO2
- The coefficient 3 in front of the carbon symbol on the right side indicates 3 carbon atoms as the bottom index 3 on the left side indicates 3 carbon atoms.
- In a chemical equation, you can change the coefficients, but never change the bottom index.
Step 5.
Next, balance the hydrogen atoms.
You have 8 on the left side. So you need 8 on the right side.
C3H8 + O2 4H2O + 3CO2
- On the right, you're now adding 4 as a coefficient because the bottom index shows that you already have 2 hydrogen atoms.
- If you multiply the coefficient of 4 by the lower index of 2, you get 8.
Finish by balancing the oxygen atoms.
- Since you've added the coefficients to the molecules on the left side of the equation, the number of oxygen atoms changes. You now have 4 oxygen atoms in a water molecule and 6 oxygen atoms in a carbon dioxide molecule. If added, the total becomes 10 oxygen atoms.
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Add the coefficient 5 to the oxygen molecule on the left side of the equation. You now have 10 oxygen molecules on each side.
C3H8 + 5O2 4H2O + 3CO2.
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The carbon, hydrogen and oxygen atoms are in balance. Your equation is complete.
Tips
If you're having trouble, you can type a chemical equation into an online balancer to balance it. Keep in mind that you won't have access to the online balancer while taking the exam, so don't depend on it
Warning
Never use fractions as coefficients in a chemical equation-because you can't make half a molecule or half an atom in a chemical reaction. To remove a fraction, multiply the entire equation (both left and right side) by the number in the denominator of your fraction
- Balance Chemical Equations Online
- How to Balance Chemical Equations