UNIT 9: STOICHIOMETRY

Section 1: What is Stoichiometry? More than 3000 silk cocoons are needed to make just one kimono. Like silk manufacturers, chemists must know how much reactant they need to make a certain amount of product. Determining the quantities of reactants and products in a reaction requires a balanced chemical equation.

Using Balanced Chemical Equations chemists use balanced chemical equations to calculate how much reactant is needed or product is formed in a reaction. stoichiometry: the calculation of quantities in chemical reactions.

Interpreting Chemical Equations A balanced chemical equation can tell the amount of: atoms, molecules, or moles; and mass. The most important info is the mol-to-mol ratios

Interpreting Chemical Equations Atoms The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2?

Interpreting Chemical Equations Molecules The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2?

Interpreting Chemical Equations Moles The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2? # of molecules = # of moles

Interpreting Chemical Equations Mass The balanced chemical equation for the formation of ammonia can be interpreted in several ways. Predicting How many molecules of NH3 could be made from 5 molecules of N2 and 15 molecules of H2?

Interpreting Chemical Equations Mass & Atoms Mass and atoms are conserved in every chemical reaction

Atoms Mass Molecules Moles 12 12 164.18 g 164.18 g 5 4 5 4 Conceptual Problem 12.1 Atoms Mass Molecules Moles 12 12 164.18 g 164.18 g 5 4 5 4

Mole Ratios A mole ratio is a ratio between the numbers of moles of any two substances in a balanced equation. Mole ratios convert moles of one substance to moles of another substance.

Mol to Mol Ratios 2 H2 + O2 → 2 H2O 2 mol H2 for every 1 mol O2

Mol to Mol Ratios 2 H2 + O2 → 2 H2O 2 mol H2 for every 2 mol H2O

2 H2 + O2 → 2 H2O There are 6 mol to mol ratios that can be written from this balanced equation: 2 mol H2 1 mol O2 2 mol H2O 1 mol O2 2 mol H2 2 mol H2 2 mol H2 1 mol O2 2 mol H2O 2 mol H2O 2 mol H2O 1 mol O2 To determine the number of moles in a sample of a compound, first measure the mass of the sample. Then use the molar mass to calculate the number of moles in that mass. 14

Mg + 2 HCl → MgCl2 + H2 1 mol H2 1 mol Mg 4.0 mol Mg x = 4.0 mol H2 Mole to Mole Conversion How many moles of hydrogen gas (H2) are produced from 4.0 mol Mg? Mg + 2 HCl → MgCl2 + H2 1 mol H2 1 mol Mg 4.0 mol Mg x = 4.0 mol H2 mol ratio 15

Mg + 2 HCl → MgCl2 + H2 1 mol H2 2 mol HCl 4.0 mol HCl x = 2.0 mol H2 Mole to Mole Conversion How many moles of hydrogen gas (H2) are produced from 4.0 mol HCl? Mg + 2 HCl → MgCl2 + H2 1 mol H2 2 mol HCl 4.0 mol HCl x = 2.0 mol H2 mol ratio 16

Quick Quiz. 1. What is conserved in the reaction shown below? H2(g) + Cl2(g)  2HCl(g) only mass only mass and atoms only mass, atoms, and moles mass, atoms, moles, and molecules

Quick Quiz. 2. What is the most important information from a chemical equation? states of matter moles of products mol-to-mol ratios of reactants and products mass of reactants

C2H5OH(l) + 3 O2(g)  2 CO2(g) + 3 H2O(g) Quick Quiz! 3. How many moles of water are produced from burning 4.00 mol of ethanol (C2H5OH)? C2H5OH(l) + 3 O2(g)  2 CO2(g) + 3 H2O(g) 3.00 mol H2O 4.00 mol H2O 12.0 mol H2O 1.33 mol H2O