1. Balancing Chemical Equations

2. Writing Chemical Equations Reactant  Products Reactant – what you start with in a chemical reaction. It is on the left side of the arrow.  - means yields or produces Product – this is what you end up with in a chemical reaction. + - and or added together HCl + NaOH  NaCl + H 2 O is read as HCl added together with NaOH yields NaCl and H 2 O

3. Other Parts of the Chemical Equation (s) – indicates a solid substance (l) – indicates a liquid substance (g) – indicates a gaseous substance (aq) – indicates an aqueous substance - indicates that heat is supplied to the reaction - indicates that a catalyst is used in the reaction Catalyst – a substance that speeds up a chemical reaction but is not used up.

4. The Skeleton Equation The skeleton equation is a chemical equation that does not indicate the relative amounts of reactants and products. It is the first step in writing a complete chemical equation Fe + O 2  Fe 2 O 3

5. Why Must the Chemical Equation Be Balanced? The law of conservation of matter states that matter cannot be created or destroyed. A chemical equation must have the same number of atoms of each element on each side. A chemical equation is like a see-saw, it doesn’t work unless both sides are balanced.

6. Balancing the Chemical Equation What is wrong with the following equation? Fe + O 2  Fe 2 O 3 To balance this equation, first write out the skeleton equation with the elements on each side underneath. Next, write out the atoms of each element on each side. Fe + O 2  Fe 2 O 3 Fe = Fe= O = O= 1 2 2 3

7. Balancing the Chemical Equation To balance the chemical equation, we must add coefficients to each side. A coefficient is a whole number placed in front of a chemical formula to balance the equation. Use trial and error to decide on the coefficients needed one compound at a time. __Fe + __O 2  __Fe 2 O 3 Fe = 1 Fe= 2 O = 2 O = 3 2 x 2=2 2 x 2=4 x 2=6 4 x 4=4 x 3=6 3

8. Balancing the Chemical Equation 4Fe + 3O 2  2Fe 2 O 3 Now that both sides have the same number of atoms, it is called a balanced equation.