1. 6.2 – NOTES Representing Reactions

2. D.3 Keeping Track of Atoms
When a car’s gas tank empties, where do the atoms in the gasoline go?
The atoms don’t just disappear
Law of conservation of matter
Matter can’t be created or destroyed in a reaction
Molecules get broken apart and rearranged but atoms will remain

3. Balanced chemical equation
Number of atoms of each element is the same on the reactant and product sides
The reactant is on the left side of the arrow
The product is on the right side of the arrow
The number of atoms must be equal on both sides

5. Subscripts
The number printed below the line of type
Tell you how many elements are present in a molecule or formula
No number means that there is one atom
Coefficients
Big numbers put in front of formulas
Tell you how many units are present in an equation
The only number you can change
You do not write a coefficient of 1

6. Molecules are the smallest unit of a covalently bonded substance
Formula unit are the smallest unit of an ionically bonded substance

7. Letters after a molecule or formula unit are for the state of matter
(s) = solid
(l) = liquid
(aq) = aqueous, dissolved in water
(g) = gas

8. D.4 Accounting for Atoms
Burning propane gas is a common source of heat for campers. The chemical equation is:
C3H8(g) + O2(g)  CO2(g) + H2O(g)
Let’s interpret this equation several ways:
Words
Propane Gas reacts with Oxygen gas to produce Carbon Dioxide and Water

9. Molecular Models
1 propane molecule oxygen molecule  1 carbon dioxide molecule + 1 water molecule
An Atom Inventory
Reactant Side Product Side
C= C =
O = O =
H = H =
Is this a balanced chemical equation?

10. D.5 Nature’s Conservation: Balanced Chemical Equations
Law of conservation of matter is based on the idea that atoms are indestructible
Extremely small amounts of matter may be converted to energy

11. YOU CANNOT CHANGE SUBSCRIPTS WHEN BALANCING- ONLY COEFFICIENTS!!!!
Steps for balancing a chemical equation
Check to see if equation is balanced (atom inventory)
Balance Polyatomic Ions (Usually in Parenthesis)
Balance Metals
Balance Non-metals except for H and O
Balance H
Balance O
Check to see if atoms are equal in both sides

12. Examples
KClO3  KCl O2

13.  Ba(NO3)2 + Na2SO4  BaSO4 + NaNO3

14. Zn HCl  H ZnCl2

15. Al Ni(NO3)2  Al(NO3) Ni

16. Reaction types A + B  AB 2 Na + Cl2  2 NaCl
Reactions are classified based on the number of reactants and products present in the reaction
Synthesis/composition reaction
Reactants- multiple reactants (2 or more)
Products- One Product
Example
 A + B  AB
2 Na + Cl2  2 NaCl

17. AB  A + B 2 KBr  2K + Br2 Decomposition reaction Reactants- one
Products- multiple (2 or more)
Example
AB  A + B
2 KBr  2K + Br2 

18. Single replacement reaction
Reactants- element and compound
Products- element and compound
Follows rules of the activity series
Example:
A + BC  B + AC
Li + AuCl  Au + LiCl

19. AB + CD  AD + CB or CB + AD (order doesn’t matter)
Double replacement reaction
Reactants- 2 compounds
Products- 2 compounds
Examples
 AB + CD  AD + CB or CB + AD (order doesn’t matter)
NaCl + HBr  HCl + NaBr

20. Combustion reaction CH4 + 2O2  CO2 + 2H2O C3H8 + 5O2  3CO2 + 4H2O
Reactants- Hydrocarbon (CxHy) and Oxygen (O2)
Products- CO2 and H2O
Examples
CH4 + 2O2  CO2 + 2H2O
C3H8 + 5O2  3CO2 + 4H2O