1. 2-2 Balancing Chemical Equations

2. In a chemical change the atoms and ions are rearranged to form new compounds with new properties.
A chemical reaction occurs when one or more chemical changes happen at the same time.
The original compounds are called reactants
The new compounds that are made are called products
Chemical reactions are represented by chemical equations.

3. Chemical Equations
Word Equation: Nitrogen monoxide + oxygen  nitrogen dioxide Symbolic Equation: 2 NO(g) + O2(g)  2 NO2 (g) What the numbers (coefficients) mean: 2 molecules NO gas react with 1 molecule O2 gas to produce 2 molecules NO2 gas

4. Chemical Equations
You must specify what state each compound in a chemical equation is in:
(g) = gas
(s) = solid
(l) = liquid
(aq) = aqueous (dissolved in water)

5. Example Equation 2 HCl + CaCO3  CaCl2 + CO2 + H2O
Identify the reactant(s)
Identify the product(s)
How many molecules of reactants are there?
How many molecules of products are there?

6. Law of Conservation of Mass
The total mass of the reactants MUST equal the total mass of the products
This is why equations must be BALANCED!

7. Balancing Equations
For an equation to be balanced, there must be an equal number of each type of atom on both sides of the reaction arrow
In other words, the number of reactant atoms MUST EQUAL the number of product atoms
We use coefficients (or numbers in front of the chemical formula) in order to balance out the numbers

8. Balancing Equations When balancing, you start with a skeleton equation
This is just the chemical formulas with no coefficients added in yet
Example:
CH4 + O2  H2O + CO2

9. Balancing Equations
Count up the number of atoms on each side of the equation
CH4 + O2  H2O + CO2
2. Add coefficients in front of the compounds until the equation is balanced.

10. Balancing Equations Order for balancing:
Metals
Non-Metals
Oxygen
Hydrogen
You don’t HAVE to balance in this order, but I find it makes it easiest!

11. Balancing Equations
Count up the number of atoms on each side of the equation
CH4 + O2  H2O + CO2
2. Add coefficients in front of the compounds until the equation is balanced.

12. __Zn + __HCl  __H2 + __ZnCl2
Balancing Equations
Try this one!
__Zn + __HCl  __H2 + __ZnCl2

13. __Fe2O3 + __CO  __Fe + __CO2
Balancing Equations
Try this one!
__Fe2O3 + __CO  __Fe + __CO2

14. Balancing Equations Assignment: Practice problems page 211
Start working through the big balancing equations worksheet booklet!