Balancing equations step by step
To balance an equation, follow five steps. One: write the correct formulas. Two: count the atoms of each element on both sides. Three: change a coefficient, a number in front of a formula, to make one element equal. Four: recount all the elements. Five: check that the numbers are the simplest whole numbers. The golden rule is: change only coefficients, never the small numbers inside formulas, called subscripts. Changing a subscript changes the substance: H₂O₂ is hydrogen peroxide, not water. Do not write a coefficient of 1. Let us balance hydrogen with oxygen: H₂ + O₂ → H₂O. Left: 2 H, 2 O. Right: 2 H, 1 O. Put 2 in front of H₂O: 2 H₂O gives 4 H and 2 O. Now hydrogen needs a 2 too: 2H₂ + O₂ → 2H₂O. Left 4 H, 2 O; right 4 H, 2 O. Balanced. Remember that only the atoms must match, not the molecules: this equation has three molecules on the left and two on the right.
| Element | Left: 2H₂ + O₂ | Right: 2H₂O |
|---|---|---|
| H | 4 | 4 |
| O | 2 | 2 |
Balance with objects. Use paper-clips (C), beads (H) and coins (O). Build the left side of C₃H₈ + O₂ → CO₂ + H₂O. Rearrange into CO₂ and H₂O, and add more O₂ molecules as needed until all the atoms are used. Write the equation you found. It should be C₃H₈ + 5O₂ → 3CO₂ + 4H₂O. Check by counting each element.