CHEM 121

Chapter 5

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The Mole• 12 eggs = • 12 bagels = • 6.02 x 1023 hydrogen atoms =• 6.02 x 1023 water molecules =

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How many water molecules are in 3.5 moles of water?

Moles of Elements in a FormulaHow many moles of each element are in 1 mole of water?

How many moles of each element are in 1 mole of glucose?

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Molar Mass

•

•

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Examples: Carbon

Atomic mass?

Molar mass?

Water

Molecular mass?

Molar mass?

Calculations with Molar MassYou measure out 10.0 g of water. How many moles of water do you have?

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If a piece of metal displaces 2.2 mL water, how many water molecules has it

displaced? (Assume the density of water is 1.0 g/mL.)

Chemical Equations

Physical Change:

Chemical Change:

Chemical Equation:

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Types of Reactions

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Mg O O+

A B+

Types of Reactions

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OHH

BA

Types of Reactions

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BA + C

•

•

BA + C D

Chemical Equations

_____________ and ___________ involved in change

1. 2. 3. 4. 5.

Ex. Reaction of magnesium solid and oxygen

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Reaction Equivalents

C3H8 (g) + 5 O2 (g) 3 CO2 (g) + 4 H2O (g)

1 molecule C3H8 reacts with _______ molecules O2

1 molecule C3H8 produces _______ molecules CO2

1 molecule C3H8 produces _______ molcules H2O

5 molecules O2 produces _______ molecules CO2

2 molecules C3H8 produces _______ molecules CO2

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Ionic Equations• Molecular equations

–

• Total ionic equations–

• Net ionic equations–

Example: HCl and NaOH

Precipitation Reactions

• Type of replacement reaction•

Example: Aqueous sodium iodide and lead (II) nitrate

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Stoichiometry

the study of mass relationships in chemical equations

Can’t compare mass to mass

Go to moles first

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Reaction Calculations

1.

2.

3.

4.

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Sample ProblemHow much carbon dioxide (in grams) is

produced when 3.00 g of ethanol (C2H6O) combusts in air?

How much oxygen gas is used up to combust 5.00 g of ethanol?

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5-minute review

How many grams of oxygen are needed to react with 1 mole of CH4 to create water?

Hint: carbon dioxide is also a product.

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Yields

• Theoretical yield:

• Actual yield: –

• Percent yield:

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Limiting Reactants

What if we have:8 scoops of ice

cream6 cherries100 mL of syrup.

How many sundaes can we make?

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Chemical Reactions Involving a Limiting Reactant

hydrazine (N2H4) and dinitrogen tetraoxide are liquids that ignite to form nitrogen gas and water vapor

How many grams of nitrogen gas form when 100. g of N2H4 and 200. g of dinitrogen tetraoxide are mixed?

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Redox Reactions• Reduction and oxidation

• Movement of e- from one reactant to another

• 2 Mg (s) + O2 (g) --> 2 MgO (s)

• LEO GER

• Reducing agent? Oxidizing agent?

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Oxidation Numbers (O.N.)

• Any element has O.N. = • 1A(1) ions = 2A(2) ions = • H ion can only = • Oxygen ion only = • Halogen ions usually = • The sum of all atoms O.N. in a compound =

Examples: ZnCl2sulfur trioxide

potassium sulfate

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3-minute review

What is the O.N. of each atom in CaCO3?

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Redox Reaction?

CaO (s) + CO2 (g) → CaCO3 (s)

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3-minute Review

What’s been oxidized in each reaction?

Cu (s) + AgNO3 (aq) → Ag (s) + Cu(NO3)2 (aq)

N2 (g) + H2 (g) → NH3 (g)

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