Writing and balancing equations

Last time

Before we start: last time, in Formula mass, balancing and ionic equations, you learned these points. Here they are again on one card. Keep them in mind, because today builds on them.

Atoms are never lost

Burn a candle, and the wax seems to disappear. But in a chemical reaction, no atoms are created or destroyed. They are only rearranged into new substances. A balanced equation shows this: the same number of each kind of atom on both sides.

Word equations and symbol equations

A word equation names the reactants and the products. For example: magnesium plus oxygen gives magnesium oxide. A symbol equation uses the formulae, so it can show the number of each particle. The reactants are on the left, the products on the right, and the arrow means it gives.

Rules for formulae

Some elements exist as molecules with two atoms: hydrogen, nitrogen, oxygen, fluorine, chlorine, bromine and iodine. Write the correct formula for every substance first. Never change a formula to make the equation balance. You balance only by putting numbers in front of the formulae. These numbers are called coefficients.

The method

First, write the correct formula of every reactant and every product. Second, count the atoms of each element on both sides. Third, put a number in front of a formula to balance one element at a time. Fourth, recount. Changing one number can unbalance another element. Fifth, add the state symbols: solid, liquid, gas, or aqueous for dissolved in water.