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Stoichiometry Chemistry Dr. May

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Moles One mole of anything contains Avogadro’s number of particles: One mole of sodium (Na) contains 6.02 x 10 23 atoms with a mass of 23 grams One mole of water (H 2 O) contains 6.02 x 10 23 molecules and a mass of 18 grams

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Molar Mass (Molecular Weight) (MW) Molar mass is the sum of the atomic masses of all the atoms in a molecule The molar mass of H 2 O is (2+16) = 18 grams The molar mass of CH 4 (methane) is (12 + 4) = 16 grams The molar mass of CO 2 is (12 + 32) = 44 grams The molar mass of N 2 is (14 + 14) = 28 grams 1 molar mass = 6.02 x 10 23 molecules = 1 mole

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Molar Ratio Zn + 2 HCl ZnCl 2 + H 2 The molar ratio is: 1 : 2 : 1 : 1 Or, 1 mole of zinc plus 2 moles of hydrochloric acid yields 1 mole of zinc chloride plus 1 mole of hydrogen gas

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Molar Ratio And Moles Zn + 2 HCl ZnCl 2 + H 2 1 : 2 : 1 : 1 1 mole of Zn has a mass of 65 grams 2 moles of HCl has a mass of 72 grams 1 mole of ZnCl 2 has a mass of 135 grams 1 mole of H 2 has a mass of 2 grams

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Molar Ratio And Moles Zn + 2 HCl ZnCl 2 + H 2 1 mole of Zn has a mass of 65 grams 2 moles of HCl has a mass of 72 grams 137 grams 1 mole of ZnCl 2 has a mass of 135 grams 1 mole of H 2 has a mass of _ 2 grams 137 grams

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Conservation Of Mass In a balanced chemical equation, the total formula mass of the reactants must always equal the total formula mass of the products

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Moles And Mass Moles = Grams MW Grams = Moles x MW

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Mole-Mass Relationship Grams = Moles x MW What is the mass of 1 mole of N 2 ? What is the mass of 3 moles of H 2 ? 2 x 14 = 28 grams 3 x 2 = 6 grams

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Mole-Mole Relationships 3 H 2 + N 2 2 NH 3 mr: 3 : 1 : 2 3 moles of H 2 (6 grams) combines with 1 mole of N 2 (28 grams) to give 2 moles of ammonia gas (34 grams) 6 grams + 28 grams = 34 grams

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Mole-Mole Relationships 3 H 2 + N 2 2 NH 3 mr: 3 : 1 : 2 moles: 6 2 4 6 moles of H 2 (12 grams) combines with 2 mole of N 2 (56 grams) to give 2 moles of ammonia gas (68 grams) 12 grams + 56 grams = 68 grams

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Mole-Mole Relationships 3 H 2 + N 2 2 NH 3 mr: 3 : 1 : 2 moles: 1.5 0.5 1 1.5 moles of H 2 (3 grams) combines with 0.5 moles of N 2 (14 grams) to give 1 mole of ammonia gas (17 grams) 3 grams + 14 grams = 17 grams

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Mole-Mole Relationships 3 H 2 + N 2 2 NH 3 mr: 3 : 1 : 2 moles: 1 0.33 0.67 1 mole of H 2 (2 grams) combines with 0.33 moles of N 2 (9.3 grams) to give 0.67 moles of ammonia gas (11.3 grams) 2 grams + 9.3 grams = 11.3 grams

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Mole-Mole Relationships 3 H 2 + N 2 2 NH 3 How many moles of nitrogen are needed to react completely with 3 moles of hydrogen ? The answer is …….. 1 mole

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Mole-Mole Relationships 3 H 2 + N 2 2 NH 3 How many moles of nitrogen are needed to react completely with 1.5 moles of hydrogen ? The answer is …….. 0.5 moles

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Mole-Mole Relationships 3 H 2 + N 2 2 NH 3 How many moles of nitrogen are needed to react completely with 6 moles of hydrogen ? The answer is …….. 2 moles

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Mole-Mole Relationships 3 H 2 + N 2 2 NH 3 How many moles of ammonia do you get when 1 mole of nitrogen is reacted completely with 3 moles of hydrogen ? The answer is …….. 2 moles

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Stoichiometry (The Matrix) MW22817 Eq.3 H 2 + N 2 2 NH 3 MR Moles grams 312 0.33 0.17 0.5 1.0 4.75.7

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Mass-Mass Relationships 3 H 2 + N 2 2 NH 3 How many grams of nitrogen are needed to react completely with 6 grams of hydrogen ? The answer is …….. 28 grams How did we know that ????

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Stoichiometry MW22817 Eq.3 H 2 + N 2 2 NH 3 MR312 Moles grams 6.0 28.0 2.01.03.0 34.0

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Mass-Mass Relationships 3 H 2 + N 2 2 NH 3 How many grams of nitrogen are needed to react completely with 12 grams of hydrogen ? The answer is …….. 56 grams

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Mass-Mass Relationships 3 H 2 + N 2 2 NH 3 How many grams of nitrogen are needed to react completely with 4.7 grams of hydrogen ? The answer is not obvious !

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Mass-Mass Relationships Shall we go to our STOICHIOMETRY Matrix ???? Away we go !!!!!!!

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Stoichiometry MW22817 Eq. 3 H 2 + N 2 2 NH 3 MR312 Moles? grams4.7 Moles = grams MW 2.350.78 1.57 2.35 Grams = moles x MW 21.926.6

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Real Stoichiometry (The Equation) H 2 + N 2 NH 3

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Real Stoichiometry (Balance Equation) 3 H 2 + N 2 2 NH 3

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Real Stoichiometry (The Molar Ratio) 3 H 2 + N 2 2 NH 3 3 1 2

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Real Stoichiometry (The Molar Mass) 2 28 17 3 H 2 + N 2 2 NH 3 3 1 2

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Real Stoichiometry (The Problem) 2 28 17 3 H 2 + N 2 2 NH 3 3 1 2 1.5 g. ? How many grams of NH 3 are made when 1.5 grams H 2 reacts completely with N 2 ?

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Real Stoichiometry (Find Moles) 2 28 17 3 H 2 + N 2 2 NH 3 3 1 2 Gr. 1.5 g. Moles ?? Moles = Grams MW Moles = 1.5 2 = 0.75

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Real Stoichiometry (Move Moles) 2 28 17 3 H 2 + N 2 2 NH 3 3 1 2 Gr. 1.5 g. Moles 0.75 ? The molar ratio of NH 3 to H 2 is 2:3 The number of moles of NH 3 is 2/3 of the moles of H 2 2/3 of 0.75 = 0.50

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Real Stoichiometry (Find Grams) 2 28 17 3 H 2 + N 2 2 NH 3 3 1 2 Gr. 1.5 g. ? Moles 0.75 0.50 Grams = moles x MW = 0.50 x 17 = 8.5

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Real Stoichiometry (The Answer) 2 28 17 3 H 2 + N 2 2 NH 3 3 1 2 Gr. 1.5 g. 8.5 g. Moles 0.75 0.50 Grams = moles x MW = 0.50 x 17 = 8.5

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Real Stoichiometry (The Solution)) 2 28 17 3 H 2 + N 2 2 NH 3 3 1 2 1.5 g. ? How many grams of NH 3 are made when 1.5 grams H 2 reacts completely with N 2 ? The answer is 8.5 grams

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The End This presentation was created for the benefit of our students by the Science Department at Howard High School of Technology Please send suggestions and comments to rmay@nccvt.k12.de.us

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