Warm Up 3/29-30 1) What type of chemical reaction is represented in the energy diagram shown below? 2) What side of the chemical equation does the energy term go on? Explain.

Unit 8: Stoichiometry Pt I The study of mass and mole relationships in chemical reactions

Objectives Given a chemical reaction stated in words, write a balanced chemical equation. Starting with a balanced chemical equation, and the number of moles of a reactant or product, determine the number of moles of any other reactant or product involved. Develop the BCA approach to analyzing mole relationships in chemical reactions.

What does a chemical equation tell you? Methane when burned in air forms carbon dioxide and water ___CH4 + ___O2  ___CO2 + ___H2O 2 What does that mean? 1 molecule of CH4 combines with 2 molecules of oxygen to form 1 molecule of CO2 and 2 molecules of H2O From our nail lab, we know it also means that: 1 mole of CH4 combines with 2 moles of oxygen to form 1 mole of CO2 and 2 moles of H2O Further, from conservation of mass, it means: 16g of CH4 combines with 64g of oxygen to form 44g of CO2 and 36g of H2O (80 g of reactants and 80 g of product)

Chemical rxns mean chemical change Using the BCA approach, we are going to analyze the reaction during three stages of the reaction: How much of each reactant and product is present in the reaction vessel just before the reaction How much change occurs in each substance during the reaction What is present in the reaction vessel immediately after the reaction is complete.

Example 1: 8.0 mol of HCl are needed for this reaction Lead will react with hydrochloric acid to produce lead(II) chloride and hydrogen gas. How many moles of hydrochloric acid are needed to completely react with 4.0 mole of lead? Equation: __Pb + __HCl  __PbCl2 + __H2 2 Before: 4.0 mol xs mol 0 mol 0 mol Change: -4.0 mol -8.0 mol +4.0 mol +4.0 mol After: 0 mol xs 4.0 mol 4.0 mol 8.0 mol of HCl are needed for this reaction

Example 2: How many moles of hydrogen gas will be produced if 2.5 moles of calcium hydride react according to the following equation? Equation: __CaH2 + __H2O  __Ca(OH)2 + __H2 2 Before: 2.5 mol xs mol 0 mol 0 mol Change: -2.5 mol -5.0 mol +2.5 mol +5.0 mol After: 0 mol xs 2.5 mol 5.0 mol 5.0 mol of H2 are produced by this reaction

Example 3: How many moles of water will be produced if 0.45 mol of oxygen reacts according to the following equation? Equation: __C6H6 + __O2  __CO2 + __H2O This ones not so easy to do in your head, lets use the mole ratios to determine amounts 2 12 15 6 Notice we used the moles given “Start with the number you are given” Now, plug these values into our BCA table

Example 3: How many moles of water will be produced if 0.45 mol of oxygen reacts according to the following equation? Equation: 2C6H6 + 15O2  12CO2 + 6H2O Before: xs 0.45 mol 0 mol 0 mol Change: -0.060mol-0.45mol +0.36 mol +0.18 mol After: xs 0 mol 0.36 mol 0.18mol So, 0.45 mol O2 with xs benzene produces 0.18 moles of water

Assignment Read Stoichiometry Handout HW: Unit 8 WS #1 Due Thursday/Friday Just Do It