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how to right a chemical equation?

Steps in Writing a Balanced Equation

Step 1. In writing a chemical reaction, the reactants and the products are written down. If the products are not known, they can be predicted in many cases.

Step 2. The formulas of each substance must be correct. The diatomic gases are hydrogen, H2, nitrogen, N2, oxygen, O2, fluorine, F2; chlorine, Cl2, bromine, Br2; and iodine, I2.

Step 3. The equation is then balanced. The balancing is done by putting a coefficient before compounds until the atoms of each element on one side of the equation equal the number of atoms of that element on the other side of the equation.

Example 1

Sodium reacts with water to produce a metallic hydroxide and hydrogen gas. Write a balanced equation for the reaction.

Solving Process:

Step 1. Write the word equation:

 sodium + water -> sodium hydroxide + hydrogen

Step 2. Write a skeleton equation.

Since hydrogen is a diatomic gas, its formula is H2. The formula for water may be written as HOH if this makes it easier to balance the equation.

 Na+ HOH -> NaOH + H2

Step 3. Balance the equation.

The metallic element sodium is balanced. One atom of sodium is on each side of the equation. There is one hydrogen atom on the reactant side (the H in OH has been accounted for) and 2 hydrogen atoms on the product side. Place a 2 in front of the HOH to balance the hydrogen atoms.

 Na + 2HOH -> NaOH + H2

There are now 2OH on the left and 1 on the right. Place a 2 in front of the NaOH to give the same number of OH on each side.

 Na + 2HOH -> 2NaOH + H2

Put a 2 in front of the sodium metal. The balanced equation reads

 2Na(c) + 2HOH(l) -> 2NaOH(aq) + H2(g)

Check visually to see if the equation is balanced, or list all the atoms (the hydroxide can be listed as OH or can be separated into H and 0).