1. Empirical Formulas and Mole Ratios

2. Why balanced chemical equations?
Balanced Chemical Equations and Mole Ratios
A balanced chemical equation tells you the mole ratios, or proportion of reactants and products, in a chemical reaction.
By looking at the coefficients of a balanced chemical equation, mole ratios can be found.

3. Law of Definite Proportions
A compound always contains the same elements in the same proportions regardless of how the compound is made or how much of the compound is formed.

4. Mole Ratios
Mole Ratios tell you the relative amounts of products to reactants.
Look at the coefficients!
2 H2O  2H2 + 1O2
2 moles of water for every 2 moles of hydrogen and 1 mole of oxygen.

5. Moles converted to masses
Molar Mass(M) is the atomic mass of each element in a molecule added together.
EX) CH4 (methane) atomic mass # of atoms total mass
C g/mol x = g/mol
H 1.01g/mol x = 4.04g/mol
Total Molecular Weight of CH4 = 16.05g/mol
Don’t Forget units
Find the Molar Mass (M) of Benzene (C6H6)
78.11g/mol
Mole ratios can be converted to masses.
Simply multiply by the molecular mass of each substance by the mole ratio from the balance equation.

6. EX) Find the mass of each element in the following equation.
2 Mg O2 
2 MgO
Amount
(mol) 2 1
Molar Mass
(g/mol)
24.3
32.0
( )
40.3
Mass Calculation
24.3g/mol x 2mol
32.0g/mol x 1 mol
40.3g.mol x 2mol
Mass
(g)
48.6g
32.0g
80.6g

7. The Law of Conservation of Mass
All elements located on the reactants side must be located on the products side, mass cannot be created or destroyed. Check your answer from the previous slide. 48.6g g = 80.6 g

8. Empirical Formula
A molecular formula is the ratio of atoms actually found in a molecule
An empirical formula is the simplest whole-number ratio of atoms in a molecule.

9. Examples Empirical Formula Molecular Formula Water H2O Salt NaCl
Glucose
CH2O
C6H12O6
Empirical & Molecular formulas can be the same.
To make an Empirical formula reduce the Molecular formula.