1. Chemical Reactions: Review

2. Calculating Molar Mass / Gram Formula Mass
Locate element on periodic table, and identify the atomic mass
Multiply the number of each element in the equation X atomic mass
Add up the total mass of each element to get the molar mass
C6H12O6
C: 6 X 12g = 72g/mol Molar Mass: = 180g/mol
H: 12 X 1g = 12g/mol
O: 6X16g = 96 g/ml

3. Mole Conversions: use your railroad tracks!
Avogadro’s #: x 1023 mlcls / mole
Given grams, asked for moles:
Find molar mass of compound
Mass compound (g) / Molar mass (g)
Given moles, asked for grams:
#moles x molar mass (g/mol)
Given moles, asked for particles (or atoms):
# moles x Avogadro’s #
Given grams, asked for particles (or atoms)
Find moles
Convert to particles

4. Calculating Percent Composition
Calculate formula weight of compound (sum all atomic weights)
Multiply atomic weight x # atoms
Divide by formula weight
Multiply by 100%
CH4
Formula weight: (1) = 16 g/mol
C: 12/16 = 0.75 * 100% = 75%C
H: (1*4)/16= 0.25 *100% = 25% H

5. Empirical Formula vs Molecular Formula
Identifies elements in simplest whole numbers (CH4)
Always used for ionic compounds
Formula weight (total sum of atoms in chemical formula)
Molecular formula
Identifies the EXACT number of atoms in a compound (C2H8)
Used to describe covalent compounds
Molecular weight (total sum of atoms in Molecular formula)

6. Calculating Empirical Formulas
If total % composition = 100, assume the %s are grams
Divide % by atomic mass of each element
Divide all by the smallest # calculated in #2
If you have a decimal….
0.5, multiply by 2
0.24, multiply by 4
0.3, multiply by 3
Answers are your subscripts for your empirical formula

7. Balancing Equations from Word Problems
Write the chemical equation
If you don’t recognize the compound, write down the elements
Look up elemental charge, “Criss-cross simplify” to identify subscripts
Inventory reactant elements and product elements
Balance so equal #s on both sides by altering coefficients only!
Hint: look for common factors!
Verify simplest coefficients used

8. Types of Reactions Decomposition: AB → A + B
Combination / Synthesis: A + B → AB
Single Replacement: AB + C → AC + B
Cation ions replace cations
Anions replace anions
Double Replacement: AB + CD → AC + BD
Ion exchange
Combustion Reaction: Hydrocarbon + O2 → CO2 + H2O