Empirical Formulas and Mole Ratios

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.

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.

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.

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 12.01g/mol x 1 = 12.01g/mol H 1.01g/mol x 4 = 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.

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 (24.3+16) 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

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 + 32.0g = 80.6 g

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.

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.