Balancing Equations

The Law of Conservation of Mass (or Matter) In a chemical reaction, matter is neither created nor destroyed.

Therefore… What begins in a chemical reaction can be found in the end of a chemical reaction. What goes in, must come out.

The Meaning of a Chemical Equation They tell us… What substances are reacting What substances are produced The ratios of substances reacting to those being produced

Reactants The reactants are on the left side of a chemical equation 2H 2 + O 2 2H 2 O Reactants

The products are on the right side Products 2H 2 + O 2 2H 2 O Product

Question? However, you might ask, "On the left and right side of what?" Answer - the arrow

2H 2 + O 2 2H 2 O On the left side are the reactants - hydrogen and oxygen On the right side is the product - water

Ca(H 2 PO 4 ) 2 + CaSO 4 + HF Ca 10 F 2 (PO 4 ) 6 + H 2 SO 4 There can be one, two, three, or more substances on either side of the arrow as in the above example.

Coefficients Coefficients are the numbers in front of the formulas. 2 H 2 + O 2 2 H 2 O

COEFFICIENTS The coefficients give the number of molecules (or atoms) involved in the reaction. In the example reaction, two molecules of hydrogen react with one molecule of oxygen and produce two molecules of water.

3 Important Things One: Reactants are on the left and products are on the right. Of what? The arrow Two: Coefficients are the numbers in front of each formula. If no number is shown, a one is understood. Three: The coefficients tell us how many molecules of each reactant used and how many molecules of each product made.

1) Zn + 2 HCl ---> ZnCl 2 + H 2 2) 2 KClO 3 ---> 2 KCl + 3 O 2 3) S F 2 ---> 8 SF 6 4) 4 Fe + 3 O 2 ---> 2 Fe 2 O 3 5) 2 C 2 H O 2 ---> 4 CO H 2 O Identify the reactants, the products and the coefficients of these equations: