Balancing Chemical Equations – Interactive PhET Simulation

Explore balancing chemical equations

A chemical equation must obey the law of conservation of mass. During a chemical reaction, atoms are rearranged, but they are neither created nor destroyed. The number of atoms of each element must therefore be the same on both sides of a balanced equation.

This interactive PhET simulation allows you to practise balancing equations while using particle diagrams, balance scales and bar charts to see why an equation is or is not balanced. It also includes increasingly challenging equations and a game to test your skills.

Predict the coefficients before changing them. Remember that you balance an equation by changing the numbers in front of formulae — never by changing the chemical formulae themselves.

Balancing Chemical Equations is provided by PhET Interactive Simulations, University of Colorado Boulder, and is used under the CC BY-NC 4.0 licence.

Try these challenges

1. Start with a simple equation
Look at the numbers of each type of atom on the left and right sides. Which elements are already balanced, and which are not?

2. Change coefficients only
Balance the equation by changing the coefficients in front of the formulae. Do not alter any subscripts in the chemical formulae.

3. Use the particle view
Compare the particle diagrams before and after balancing. How does the balanced equation show that atoms are rearranged rather than created or destroyed?

4. Use the balance tools
Switch on the balance scales or bar charts. Can you use them to identify quickly which element is causing an equation to be unbalanced?

5. Work systematically
Try balancing a more complicated equation. Which element is most useful to balance first? Which element is best left until last?

6. Check the simplest ratio
Once an equation is balanced, check whether all the coefficients can be divided by the same whole number. Chemical equations should normally be written using the smallest whole-number ratio.

7. Test yourself
Use the game section and try to balance each equation before using any visual aids. Then use the simulation to check your answer.

The key question

Keep asking:

Have I got the same number of atoms of every element on both sides of the equation?

That is the essential test for whether a chemical equation is balanced.

 
 
 
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