A chemical equation shows what happens in a chemical reaction. As in any equation, the elements on the left side of the equation (the reactants) must equal the elements on the right (the products). Here are just a few things to remember when balancing chemical equations:

• Same elements in equal numbers: For an equation to be balanced, it must have the same number of each element on each side of the equation. The mass of the reactants has to equal the mass of the products — remember the law of conservation of mass?

• Same charge: If there’s a net charge on one side of the equation, the other side of the equation must have the same charge.

• Unchanged chemical formulas: Most importantly, never alter a chemical formula! Subscripts (and superscripts for that matter) do not magically change. Change only the coefficients.