Chemical Reactions

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Chemical Reactions

• 1. Formula Mass
• 2. Moles
• 3. Calculating Moles
• 4. Chemical Changes
• 5. Chemical Rxn
• 6. Energy Chem Rxn
• 7. Reaction Rate
• 8. Calculating Reactants Products

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Formula Mass

• 1. Atomic mass is expressed in atomic mass units,
  amu
• 2. H atoms mass defined as 1 amu
• 3. Other elements atomic masses are calculated
  relative to H
• 4. To find the mass of molecule or polyatomic
  ion, add up all atomic masses of all its
  constituent atoms

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Formula Mass, water, H2O
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Formula Mass, 2,3 butanedione, C4H6O2
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Formula Mass, Calcium nitrate, Ca(NO3)2
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Diatomic Elements

• 1. Seven elements occur as diatomic molecules in
  their elemental state
• 2. H2, O2, N2, F2, Cl2, Br2, I2
• 3. Elemental hydrogen would have a formula mass
  of 2amu
• 4. Elemental oxygen would have a formula mass of
  32amu . . .

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Gay-Lussacs Experiments

• 1. Compared measured volumes of gas reactants
  products
• 2. Conclusion- At STP, the volumes of reacting
  gases gas products are expressed in whole
  number ratios

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Avogadros Hypothesis

• 1. Atomic mass is directly proportional to actual
  mass for equal volumes
• 2. Let amu atomic mass
• g actual mass
• then k x amu g
• k g/amu of atoms

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Avogadros Number

• 1. Reasoned of atoms, molecules, or ions of
  equal volumes must be a constant number
• 2. Made calculations of atomic mass possible by
  using density
• 3. 6.023 x 1023 atoms/l at STP

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Mole

• 1. A mole of any substance, at STP, contains the
  same of particles (atoms/molecules/ions) as a
  mole of any other substance
• 2. The mass of a mole will be the substances
  atomic or formula mass in grams

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Mole Example 1

• Q- What would be the mass of 1 mole of S?
• A- Atomic mass S 32.07amu, so

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Mole Example 2

• Q- What would be the mass of 0.563 mole of K?
• A- Atomic mass K 39.10amu, so

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Mole Example 3

• Q- What would be the mass of 2.31 moles of H2?
• A- Formula mass H2 2.02amu, so

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Physical Changes

• 1. Intrinsic properties of substance remain
  unchanged
• 2. Phase changes- solid to liquid to gas

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Chemical Changes

• 1. Form new substances with different properties
  from old
• 2. Substance changes
• 3. AB CD ? AD CB
• (reactants) (products)

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Reactions Energy

• 1. All substances possess Ep because of their
  composition structure
• 2. This Ep is referred to as chemical energy, Ec
• 3. Chem rxn always results in an energy change,
  DE
• 4. Products of chem rxn have different structure
  composition, therefore different Ep

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Endothermic

• 1. If Ep reac lt Ep prod, then energy absorbed
• 2. Rxn was endothermic
• 3. Photosynthesis
• 4. Production of CS2

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Exothermic

• 1. If Ep reac gt Ep prod, then energy liberated
• 2. Rxn was exothermic
• 3. Oxidation of wood or any fuel

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Chemical Equations

• 1. Reactants ? Products
• 2. Reactants Energy ? Products
• 3. Reactants ? Products Energy
• 4. 1st Law of Thermodynamics- mass energy are
  conserved

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Balancing Chem Eq

• 1. Change coefficients, never change subscripts
• 2. Coefficients must be whole numbers, but . . .
• 3. Practice, practice, practice

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Chem Eq Example 1

• CH4 O2 ? CO2 H2O

CH4 2O2 ? CO2 2H2O
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Chem Eq Example 2

• CH4 O2 ? CO H2O

CH4 O2 ? CO 2H2O
CH4 1.5O2 ? CO 2H2O
2CH4 3O2 ? 2CO 4H2O
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Chem Eq Example 3

• Ca(OH)2 H3PO4 ? Ca3 (PO4)2 H2O

3Ca(OH)2 H3PO4 ? Ca3 (PO4)2 H-OH
3Ca(OH)2 2H3PO4 ? Ca3 (PO4)2 H-OH
3Ca(OH)2 2H3PO4? Ca3 (PO4)2 6H-OH
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Reaction Rate

• 1. Amt of reactant used up or amt of product
  formed per unit of time
• 2. Increase concentration, increase temperature,
  catalysts
• 3. Keq

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Mole Calculations

• 1. How many grams of reactant are needed to
  produce a given amt of product?
• 2. How many grams of product can be produced from
  a given amt of reactant?
• 3. Steps

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Mole Calculation Steps

• 1. Write balanced equation molar ratios
• 2. Calculate formula or atomic masses
• 3. Convert grams of known substance to moles
• 4. Molar ratio factor
• 5. Convert unknown substance from moles to grams
• 6. Cancel calculate

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Mole Calc, Example 1

• Q- At high T, iron III oxide reacts with carbon
  to from iron carbon monoxide. How many grams
  of carbon will be needed to reduce 1kg of iron
  III oxide?

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Mole Calc, Example 1, Step 1

• Write balanced equation molar ratios

Fe2O3 C ? Fe CO
Fe2O3 C ? 2Fe CO
Fe2O3 C ? 2Fe 3CO
Fe2O3 3C ? 2Fe 3CO
1mole 3mole ? 2mole 3mole
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Mole Calc, Example 1, Step 2

• Calculate formula mass, Fe2O3

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Mole Calc, Example 1, Step 2

• Calculate atomic mass, C

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Mole Calc, Example 1, Step 3

• Convert grams of known to moles

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Mole Calc, Example 1, Step 4

• Molar ratio factor

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Mole Calc, Example 1, Step 5

• Convert unknown from moles to grams

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Mole Calc, Example 1, Step 6

• Cancel calculate

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Mole Calc, Example 2

• Q- At high T, iron III oxide reacts with carbon
  to from iron carbon monoxide. How many grams
  of iron can be produced from 1kg of iron III
  oxide and sufficient carbon?

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