How to balance chemical equations. When pieces of matter come together or break apart, it is called a reaction. The law of conservation of matter states that matter can not be created or destroyed. In any reaction, you must have the same amount of each part before and after the reaction happens. We show how reactions become balanced by using chemical equations.

How to balance chemical equations. 2Na + Cl2 2NaCl This is a balanced chemical equation.

How to balance chemical equations. 2Na + Cl2  2NaCl The arrow is called the yields sign. It separates what you start with on the left from what you end up with on the right.

How to balance chemical equations. 2Na + Cl2  2NaCl To the left of the yields sign are the parts that react. They are called the reactants.

How to balance chemical equations. 2Na + Cl2  2NaCl To the right of the yields sign is what you end up with after the reaction. These are called the products.

How to balance chemical equations. 2Na + Cl2  2NaCl The little number next to and below an element is called a subscript. We have been using them all along. We never change subscripts in a chemical equation.

How to balance chemical equations. 2Na + Cl2  2NaCl The big numbers next to the elements or compounds are called coefficients. These are the only things we can change in a chemical equation.

How to balance chemical equations. 2Na + Cl2  2NaCl Coefficients tell us the amount of each compound or element we have. You multiply the subscript for each element to the right of a coefficient until you are stopped by a + or 

How to balance chemical equations. 2Na + Cl2  2NaCl So in this equation you have 2 x 1 sodium atoms being added to 2 chlorine atoms yielding 2 x 1 sodium chloride molecules.

How to balance chemical equations. ___H2 + ___O2 ___H2O When we balance chemical equations, we need to figure out what coefficients to use.

How to balance chemical equations. ___H2 + ___O2 ___H2O To do that, we list how many atoms of each element we start with, then use math to figure out the coefficients.

How to balance chemical equations. ___H2 + ___O2 ___H2O In this equation, we start with: Reactants Products H = 2 O = 2 O = 1

How to balance chemical equations. ___H2 + ___O2 ___H2O Our hydrogen is balanced, but we don’t have enough oxygen in the product. Reactants Products H = 2 O = 2 O = 1

How to balance chemical equations. ___H2 + ___O2 ___H2O We need to make our best mathematical guess as to which coefficient will bring balance to the equation. Reactants Products H = 2 O = 2 O = 1

How to balance chemical equations. ___H2 + ___O2  ___ H2O 2 We need two oxygen atoms, so lets try a coefficient of 2 in front of the product. Reactants Products H = 2 O = 2 O = 1

How to balance chemical equations. ___H2 + ___O2  ___ H2O 2 Multiply that 2 by the subscripts for each atom in the product. Reactants Products H = 2 H = O = 2 O = 4 2

How to balance chemical equations. ___H2 + ___O2  ___ H2O 2 Now we have enough oxygen, but too much hydrogen. How do we balance it? Reactants Products H = 2 H = O = 2 O = 4 2

How to balance chemical equations. ___H2 + ___O2  ___ H2O 2 2 If we put a coefficient of 2 in front of the H2 on the reactants side, we can balance the equation. Reactants Products H = O - 2 O = 4 4 2

How to balance chemical equations. Multiply the number of atoms you have by coefficients to balance equations. Multiply coefficients by every subscript until you hit a + or a . Never, ever, EVER change a subscript. Make a list of how much of each atom you have and change it as you add coefficients to your equation. If there are poly-atomic ions on both sides of your equation, don’t separate them!

___Al(OH)3 + ___H2SO4 ___Al2(SO4)3 + ___ H2O Quick Check ___Al(OH)3 + ___H2SO4 ___Al2(SO4)3 + ___ H2O