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J Unit 3 Chemical Reactions 3.6 What is stoichiometry? February 16, 2011 DO NOW: 1. What is the mass of 4.5mol of KOH (1) 0.080g (2)36g (3) 56g (4)227g AIM : How do we use stoichiometry to determine how much reactants we need to produce a certain amount of products? 1.Find GRAM FORMULA MASS= MOLECULAR MASA K = 39.102 O = 15.999 H = 1.00794 total = 56.10894 amu per mole = 56.10894g/mol ~ 56g/mol ANSWER: 56g/mol x 4.05mol = 226.8

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What are the coefficients in a chemical equation? COEFFICIENTS: represent relative amounts of reactants and products. Coefficients also represent mole ratios in balanced equations.

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BALANCED EQUATION Balanced chemical equation: C 2 H 6 + O 2 CO 2 + H 2 O Moles C 2 H 6 Moles O 2 Moles CO 2 Moles H 2 O 4 KEY IDEA: Regardless of the number of moles of any of the reactants or products, the ratio must remain 2:7:4:6 for this reaction 2 7 4 6 274 6 148 12 13.523

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Stoichiometry Stoichiometry is the math behind chemistry…. It tells us the relationship between reactants And products in a balanced equation. EXAMPLE: How much can be produced given the amount of reactants.

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EXAMPLE How many moles of water will be produced when 3.0 mol of C 2 H 6 reacts with oxygen? __C 2 H 6 + __O 2 __CO 2 + __H 2 O 4627

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STEP 1 Use the balanced equation to determine the mole ratio between two compounds. (this case, C 2 H 6 and water H 2 O) Mole Ratios Moles __C 2 H 6 + __O 2 __O 2 + __H 2 O 4627 4627 3 ?

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STEP 2. Set up a proportion: between the known moles of compound C 2 H 6 (3 mol) and the coefficient of C 2 H 6 and moles of water (x) and the coefficient of water. 2 mol C 2 H 6 = 6 mol H 2 O 3 mol C 2 H 6 x Mole Ratios Moles __C 2 H 6 + __O 2 __O 2 + __H 2 O 4627 62 3 ?

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STEP 3. Cross Multiply Solve for the number of moles of H 2 O (x) by cross multiplying. x = (3 mol C 2 H 6 )(6 mol H 2 O) 2 mol C 2 H 6 x = 9 mol H2O (3 mol C 2 H 6 )(6 mol H 2 O) 2 mol C 2 H 6 = 6 mol H 2 O 3 mol C 2 H 6 x (x) 2 mol C 2 H 6 = 2 mol C 2 H 6

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ANSWER How many moles of water will be produced when 3.0 mol of C 2 H 6 reacts with oxygen? 9 mol of water will be produced when 3.0 mol of C 2 H 6 reacts with oxygen.

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LETS TRY SOME 1. Given the reaction 4Al + 3O 2 2Al 2 O 3, what is the minimum number of moles of oxygen gas required to produce 1 mol of aluminum oxide? 4Al + 3O 2 2Al 2 O 3 4 3 2 ? 1 3 mol O 2 x = 2 mol Al 2 O 3 1 mol Al 2 O 3 (3 mol O 2 ) (1 mol Al 2 O 3 ) = (x) (2 mol Al 2 O 3 ) (3 mol O 2 ) (1 mol Al 2 O 3 ) = (x) (2 mol Al 2 O 3 ) (x) = 1.5mol

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Lets Try Some 2.Given the reaction 4NH 3 + 5O 2 4NO + 6H 2 O, what is the maximum number of moles of H 2 O that can be produced when 2 mol of NH 3 are completely reacted? 4NH 3 + 5O 2 4NO + 6H 2 O 4 5 46 2 ? 4 mol NH 3 2 mol NH 3 = 6 mol H 2 O x (6 mol H 2 O ) (2 mol NH 3 ) = (x) (4 mol NH 3 ) (6 mol H 2 O ) (2 mol NH 3 ) = (x) (4 mol NH 3 ) (x) = 3 mol

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Complete the Independent Practice -IP will be collected at the end of class!!! -MAKE UP UNIT 3 QUIZ -Make up LABS!! Come see me if you are missing any

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