1. Chemical Quantities Chapter 9 Stoichiometry

2. Agenda 2-6-09 DN: None HW: read pp.251-253 and answer problems 3 and 4 on pp. 281 and 282( Due Monday) Objectives: Finish experiment, understand the molecular and mass information given in a balanced equation, use balanced equation to determine the relationship between moles of reactants and moles of products Upcoming : Ind. Lab Report ( Monday) 2 nd Quiz: Types of reactions ( Tuesday)

3. Stoichiometry In greek, stoicheion means element Measure the elements Refers to the quantitative relationship between reactants and products in a chemical reaction

4. Mole to Mole Conversion Consider the reaction below N 2(g) + H 2(g) ----> NH 3(g) N 2(g) + 3H 2(g) ----> 2NH 3(g) At the molecular level,it can be interpreted as: 1moleculeN 2 + 3 moleculesH 2 ---> 2 molecules NH 3 At the mole level, 1mol N 2 + 3 mol H 2 ----> 2mol NH 3

5. Note: Mole ratios in balanced equation are very important in calculating the amounts of reactants and products Ex: What is the molar ratio of N 2 /H 2, N 2 /NH 3, H 2 /NH 3 in the equation below N 2 + 3H 2 ------> 2NH 3 N 2 /H 2 = 1: 3 N 2 /NH 3 = 1:2 H 2 /NH 3 = 3: 2

6. Mole to mole Conversion Problems Consider the reaction : NH 3 + O 2 ---> N 2 + H 2 O How many moles of O 2 are needed to react with 8 moles of NH 3 ? Solution: Step1: Balance the equation 4NH 3 + 3O 2 ------> 2 N 2 + H 2 O Step2: Find the molar ratio of NH 3 to O 2 4moles NH 3 : 3 moles O 2 Step3 : Use the molar ratio of NH 3 : O 2 as a conversion factor

7. 8 moles NH 3 X 3 moles O 2 = 6 moles O 2 4 moles NH 3

8. Practice Problem Consider the reaction below H 2 O 2 ----> H 2 O + O 2 How many moles of H 2 O can be produced from 5moles of H 2 O 2 ?