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Combination reactions have fewer products than reactants:2Mg(s) + O2(g) 2MgO(s)

Mg has combined with O2 to form MgO

Categories:1. Metal + O2 Metal oxide (Mg + O2)

2. Nonmetal + Nonmetal covalent compound (ammonia formation)3. Metal + Nonmetal (other than O2) salt (Mg + Cl2)

4. Metal oxide + H2O metal hydroxide (NaOH)

5. Nonmetal oxide + H2O oxyacid (CO2 + H2O)

6. Metal oxide + Nonmetal oxide salt (Na2O + SO2)

3.2: Some Simple Patterns of Chemical Reactivity

no change in

charge on central

atom

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Decomposition Reactions have fewer reactants than products:

2NaN3(s) 2Na(s) + 3N2(g) (the reaction that occurs in an air bag)

NaN3 has decomposed into Na and N2 gas

Categories:1. Binary Compound elements (NaCl ) (don’t forget diatomics!)

2. Metal Carbonate metal oxide + CO2 (Na2CO3)

3. Metal hydroxide metal oxide + H2O (NaOH)

4. Metal chlorate chloride salt + O2 (NaClO3)

5. Oxyacid nonmetal oxide + H2O (H2CO3)

These are the opposite of the combination reactions

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Combination and Decomposition Reactions

Text, P. 80

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Combustion in AirCombustion is the burning of a substance in oxygen from air:C3H8(g) + 5O2(g) 3CO2(g) + 4H2O(l)

Hydrocarbon + O2 CO2 + H2O (complete combustion)

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• Examples # 13 & 11 (WS) and classification/prediction practice (WS)

NaCl

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Formula and Molecular Weights• Formula weights (FW): sum of AW for atoms in a formula

FW (H2SO4) = 2AW(H) + AW(S) + 4AW(O)= 2(1.01 amu) + (32.06 amu) + 4(16.00 amu)

= 98.08 amu

• Molecular weight (MW) is the weight of the molecular formula

MW(C6H12O6) = 6(12.01 amu) + 12(1.01 amu) + 6(16.00 amu)

= 180.18 amu

3.3: Formula Weights

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Percentage Composition from Formulas

• Percent composition is the atomic weight for each element divided by the formula weight of the compound multiplied by 100:

• Don’t forget hydrates!

100

Compound ofFW AWElement of Atoms

Element %

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• Examples # 15, 17, 19

Prentice Hall © 2003 Chapter 3

Mole: convenient measure chemical quantities.• 1 mole of something = 6.0221367 1023 of that thing• Experimentally, 1 mole of 12C has a mass of 12 g

Molar Mass• Molar mass: mass in grams of 1 mole of substance • (units of g/mol, g*mol-1)• Mass of 1 mole of 12C = 12 g

3.4: The Mole

Text, P. 88

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• Examples # 25 & 26

Prentice Hall © 2003 Chapter 3

Text, P. 88

Prentice Hall © 2003 Chapter 3

This photograph shows one mole of solid (NaCl), liquid (H2O), and gas (N2).

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Interconverting Masses, Moles, and Number of Particles

• Molar mass: sum of the molar masses of the atoms:molar mass of N2 = 2 (molar mass of N)

• Periodic table

• Formula weights are numerically equal to the molar mass

Text, P. 90

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Relating particles, Mass and Moles

Molar mass (g)

6.02x1023 particles

1 mole

Molecules (molecular compounds)

Formula Units (ionic compounds)

Atoms (elements)

ionsare

made of

atoms

are made of

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Macroscale vs. Microscale Interpretations of the Mole

1 formula unit of NaCl

1 mole of Cl- ions

1 mole of Na+ ions

1 ion of Na+

1 ion of Cl-

Microscale

1 mole of NaCl

Macroscale

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• Examples # 27, 29, 33 & 35