1. Unit 9 - Chemical Reactions
Balancing Chemical Reactions (Before Break)
Types of Chemical Reactions (After Break)
Test will be December 9th
Bring latitude tomorrow
Get out your notes

2. Chemical Reactions
Process in which one or more substances are converted into new substances with different physical and chemical properties

3. Reactant – substance(s) that enter into a chemical reaction
Product – substance(s) that is produced by a chemical reaction

4. A chemical reaction occurs when reactants change into products
Reactants  Products

5. Reasons for Reactions
Atoms exchanging or sharing electrons to obtain full set of valence electrons
New substances are produced as existing bonds are broken, atoms rearranged, and new bonds formed
Transfer of energy

6. Chemical Equations
Like Math
Word equation problems
Formula equation problems

7. Word equation example
Calcium reacts with oxygen to produce () calcium oxide

8. Formula equation example
Chemical symbols and formulas
Ca + O2  CaO
IMPORTANT: must use correct symbols and formulas!

9. BrINClHOF
H2 – hydrogen
O2 – oxygen
F2 – fluorine
Br2 – bromine
I2 – iodine
N2 – nitrogen
Cl2 - chlorine
These are gases that form a diatomic molecule when found in nature (or in a reaction!)
Always write them in an equation with a subscript of 2 (i.e., O2, N2, etc.)

10. To write a complete reaction, states of matter must be included for reactants and products
Solid (s)
Liquid (l)
Gas (g)
If dissolved in water, Aqueous (aq)

11. Symbols Used in Chemical Equations
Yields: indicates result of reaction
Reversible reaction
Indicates a precipitate (solid)
Indicates a gaseous product
(s) Reactant or product in a solid state
(l) Reactant or product in a liquid state
(g) Reactant or product in a gaseous state
(aq) Reactant or product in a aqueous state
Reactants are heated
Presence of a catalyst Pt

12. Balancing Chemical Equations
Remember: law of conservation of matter must be obeyed!
The number of atoms of each element must be the same before and after the reaction

13. Coefficients
Whole numbers written before the formulas for reactants and products
They are used to balance the equation
Example:
2X, where 2 is the coefficient

14. Subscripts are NEVER changed in the formula for reactants or products
These are set by the charges on the ions or the number of atoms in molecule

15. Methane reacts with oxygen to produce carbon dioxide and water
CH4 + O2  CO2 + H2O
List # of each atom
1 C  1 C
4 H 2 H
2 O 3 O
How can you make them equal, by using only coefficients?

16. Steps to Balance an Equation
Step 1: List all the elements in the equation underneath the center of the equation
Step 2: Count how many of each element is on the reactant side then the product side
Step 3: Is this balanced or unbalanced?
Step 4: Balance the equation if necessary by adding coefficients only. Never change subscripts!!!