stoichiometry chemistry dr. may. moles one mole of anything contains avogadro’s number of...
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Stoichiometry
ChemistryDr. May
Moles
• One mole of anything contains Avogadro’s number of particles:
• One mole of sodium (Na) contains 6.02 x 1023 atoms with a mass of 23 grams
• One mole of water (H2O) contains
• 6.02 x 1023 molecules and a mass of 18 grams
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 H2O is (2+16) = 18 grams
• The molar mass of CH4 (methane) is (12 + 4) = 16 grams
• The molar mass of CO2 is (12 + 32) = 44 grams
• The molar mass of N2 is (14 + 14) = 28 grams
• 1 molar mass = 6.02 x 1023 molecules = 1 mole
Molar Ratio
• Zn + 2 HCl ZnCl2 + H2
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
Molar Ratio And Moles
• Zn + 2 HCl ZnCl2 + H2
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 ZnCl2 has a mass of 135 grams
• 1 mole of H2 has a mass of 2 grams
Molar Ratio And Moles
• Zn + 2 HCl ZnCl2 + H2
• 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 ZnCl2 has a mass of 135 grams• 1 mole of H2 has a mass of _ 2 grams 137 grams
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
Moles And Mass
Moles = Grams MW
Grams = Moles x MW
Mole-Mass Relationship
Grams = Moles x MW
• What is the mass of 1 mole of N2 ?
• What is the mass of 3 moles of H2 ?
• 2 x 14 = 28 grams
• 3 x 2 = 6 grams
Mole-Mole Relationships
3 H2 + N2 2 NH3
mr: 3 : 1 : 2
• 3 moles of H2 (6 grams) combines with
• 1 mole of N2 (28 grams) to give
• 2 moles of ammonia gas (34 grams)• 6 grams + 28 grams = 34 grams
Mole-Mole Relationships
3 H2 + N2 2 NH3mr: 3 : 1 : 2moles: 6 2 4
• 6 moles of H2 (12 grams) combines with
• 2 mole of N2 (56 grams) to give• 2 moles of ammonia gas (68 grams)• 12 grams + 56 grams = 68 grams
Mole-Mole Relationships
3 H2 + N2 2 NH3mr: 3 : 1 : 2moles: 1.5 0.5 1
• 1.5 moles of H2 (3 grams) combines with
• 0.5 moles of N2 (14 grams) to give
• 1 mole of ammonia gas (17 grams)• 3 grams + 14 grams = 17 grams
Mole-Mole Relationships
3 H2 + N2 2 NH3mr: 3 : 1 : 2moles: 1 0.33 0.67
• 1 mole of H2 (2 grams) combines with
• 0.33 moles of N2 (9.3 grams) to give
• 0.67 moles of ammonia gas (11.3 grams)• 2 grams + 9.3 grams = 11.3 grams
Mole-Mole Relationships
3 H2 + N2 2 NH3
How many moles of nitrogen are needed to react completely with 3 moles of hydrogen ?
The answer is …….. 1 mole
Mole-Mole Relationships
3 H2 + N2 2 NH3
How many moles of nitrogen are needed to react completely with 1.5 moles of hydrogen ?
The answer is …….. 0.5 moles
Mole-Mole Relationships
3 H2 + N2 2 NH3
How many moles of nitrogen are needed to react completely with 6 moles of hydrogen ?
The answer is …….. 2 moles
Mole-Mole Relationships
3 H2 + N2 2 NH3
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
Stoichiometry (The Matrix)
MW 2 28 17
Eq. 3 H2 + N2 2 NH3
MR
Moles
grams
3 1 2
0.330.170.5
1.0 4.7 5.7
Mass-Mass Relationships
3 H2 + N2 2 NH3
How many grams of nitrogen are needed to react completely with 6 grams of hydrogen ?
The answer is …….. 28 gramsHow did we know that ????
Stoichiometry
MW 2 28 17
Eq. 3 H2 + N2 2 NH3
MR 3 1 2
Moles
grams6.0 28.0
2.01.03.0
34.0
Mass-Mass Relationships
3 H2 + N2 2 NH3
How many grams of nitrogen are needed to react completely with 12 grams of hydrogen ?
The answer is …….. 56 grams
Mass-Mass Relationships
3 H2 + N2 2 NH3
How many grams of nitrogen are needed to react completely with 4.7 grams of hydrogen ?
The answer is not obvious !
Mass-Mass Relationships
• Shall we go to our STOICHIOMETRY Matrix ????
• Away we go !!!!!!!
Stoichiometry
MW 2 28 17
Eq. 3 H2 + N2 2 NH3
MR 3 1 2
Moles ?
grams 4.7
Moles = grams MW2.35 0.78 1.572.35
Grams = moles x MW 21.9 26.6
Real Stoichiometry (The Equation)
H2 + N2 NH3
Real Stoichiometry (Balance Equation)
3 H2 + N2 2 NH3
Real Stoichiometry (The Molar Ratio)
3 H2 + N2 2 NH3
3 1 2
Real Stoichiometry (The Molar Mass)
2 28 173 H2 + N2 2 NH3
3 1 2
Real Stoichiometry (The Problem)
2 28 173 H2 + N2 2 NH3
3 1 2 1.5 g. ?
• How many grams of NH3 are made when 1.5 grams H2 reacts completely with N2 ?
Real Stoichiometry (Find Moles)
2 28 173 H2 + N2 2 NH3
3 1 2Gr. 1.5 g.Moles ??
Moles = Grams MW
Moles = 1.5 2 = 0.75
Real Stoichiometry (Move Moles)
2 28 173 H2 + N2 2 NH3
3 1 2Gr. 1.5 g.Moles 0.75 ?
The molar ratio of NH3 to H2 is 2:3
The number of moles of NH3 is 2/3 of the moles of H2
2/3 of 0.75 = 0.50
Real Stoichiometry (Find Grams)
2 28 173 H2 + N2 2 NH3
3 1 2Gr. 1.5 g. ?Moles 0.75 0.50
Grams = moles x MW = 0.50 x 17 = 8.5
Real Stoichiometry (The Answer)
2 28 173 H2 + N2 2 NH3
3 1 2Gr. 1.5 g. 8.5 g.Moles 0.75 0.50
Grams = moles x MW = 0.50 x 17 = 8.5
Real Stoichiometry (The Solution))
2 28 173 H2 + N2 2 NH3
3 1 2 1.5 g. ?
• How many grams of NH3 are made when 1.5 grams H2 reacts completely with N2 ?
• The answer is 8.5 grams
The End
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