prentice hall © 2003chapter 3 combination reactions have fewer products than reactants: 2mg(s) + o...
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Prentice Hall © 2003 Chapter 3
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
Prentice Hall © 2003 Chapter 3
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
Prentice Hall © 2003 Chapter 3
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)
Prentice Hall © 2003 Chapter 3
• Examples # 13 & 11 (WS) and classification/prediction practice (WS)
NaCl
Prentice Hall © 2003 Chapter 3
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
Prentice Hall © 2003 Chapter 3
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 %
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
Prentice Hall © 2003 Chapter 3
This photograph shows one mole of solid (NaCl), liquid (H2O), and gas (N2).
Prentice Hall © 2003 Chapter 3
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
Prentice Hall © 2003 Chapter 3
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
Prentice Hall © 2003 Chapter 3
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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