Stoichiometry Chemistry Dr. May. Moles One mole of anything contains Avogadro’s number of...

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


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


• 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


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


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


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


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


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


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


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


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


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 !


• 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

• This presentation was created for the benefit of our students by the Science Department at Howard High School of Technology

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Stoichiometry Chemistry Dr. May. Moles One mole of anything contains Avogadro’s number of...

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