CHM 1020

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CHM 1020

• Lecture 5
• Chemical Reactions Quantities

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Chemical change occurs when the chemical
identity of a substance is destroyed and a new
substance forms. Five possible indicators of
chemical reactions are
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States of Matter Abbreviations
2 H2(g) O2(g) 2 H2O(g
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Chemical Reactions

• Reactants
• Products
• Rules for balancing chemical equations
• Determine the correct formula for reactants and
  products
• Count the number of atoms of each element in the
  reactant and product.
• Balance the elements one at a time by using
  coefficients (number that appears in front of a
  formula in an equation---IF YOU DONT SEE A
  NUMBER IT IS 1). Never change the subscripts in
  a chemical formula of a substance
• Begin balancing equations with elements other
  than hydrogen or oxygen
• Check that each atom is balanced on both sides of
  the equation. Recall that if you have a
  parentheses around a compound, you need to
  distribute the atom. For example, Mg(CO3)2 ?
  Mg 1 atom C 1 X 2 atoms O 3 X 2 atom
• If you have the following 2 Mg(CO3)2
• Mg 2
• C 4
• O 12

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Balancing equations

• Li3N ? Li N2
• Mg N2 ? Mg3N2
• MgCl2 AgNO3 ? Mg(NO3)2 AgCl

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Types of Chemical Equations

• Combination/Synthesis
• 2 reactants, 1 product
• Ex 2 Na(s) Cl2(g) ?2 NaCl (s)
• Decomposition
• 1 reactant, 2 or more products
• Ex H2O(l) ? H2 (g) O2 (g)

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• Single- Replacement (SR/SD)
• An element and an ionic compound (acid) switch
• Activity Series of Elements (see handout)
• To predict product
• Break element and compound into its ions
• Look at the Activity series to see if the
  reaction can occur
• If it can, then criss cross OPPOSITE charges

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Examples

• Ca HCl ? ?
• Break element/compound into its ions
• Ca 2 H 1
• Cl
  -1
• Can Ca replace H? Yes
• Criss cross opposite charges
• Ca 2 Cl -1 H 1

2
1
CaCl2
H2
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Example

• Cu AgNO3 ?
• Zn Pb(NO3)2 ?
• Al CuSO4?
• Li NaCl ?

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Double Displacement

• 2 compounds(ionic/acid) 2 compounds
  (ionic/acid) ?
• A solid ionic compound (precipitate)
• and an ionic compound or acid
• To predict product
• Same as single replacement
• No need to look at the activity series
• Neutralization reaction (acid base ? water
  salt)

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Examples

• AgNO3 H2S ?
• Break into ions
• Ag 1 H 1
• NO3 -1 S -2
• Criss cross opposite charges
• Ag 1 S-2 (Ag2S)
• H1 NO3 -1 (HNO3)

1
2
1
1
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Examples

• Pb(NO3)2 KCl ?
• Mg(OH)2 HBr ?
• NH4Cl AgNO3 ?
• Na2CO3 CaSO4 ?

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OXIDATION/REDUCTION

• Oxidation losing electrons (more positive)
• Reduction gaining electrons (more negative)
• Elements in their elemental state have an
  oxidation state of zero. In a compound, break it
  into its ions.
• Examples
• Zn(s) Cu 2 (aq) ? Zn 2 (aq) Cu(s)
• Zn(s) ? Zn 2 (aq)
• Cu 2 (aq)? Cu(s)

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Determine what is oxidized/reduced

• 3Mg(s) 2 Fe3 (aq) ? 3 Mg 2 (aq) 2 Fe(s)
• Cu(s) 2 Ag 1 (aq) ? Cu 2 (aq) 2 Ag (s)
• Fe(s) 2 H (aq) ? H2(g) Fe 2 (aq)

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Mole

• Number of particles
• 1 mole number of atoms in exactly 12 g of
  carbon-12.
• 1 mole 6.02 X 10 23 atoms
• 1 mole 6.02 X 10 23 molecules
• 1 mole 6.02 X 10 23 formula units
• 1 mol 22.4 L _at_ STP (273K, 1 atm)
• 1 mol X grams (MOLAR MASS)

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Molar mass (g/mol)

• Atomic mass
• Mass of 1 atom
• Molecular mass
• Mass of a molecule
• Formula mass
• Mass of an ionic compound
• To determine molar mass
• Atoms X atomic mass

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Atoms in a formula

• (NH4)2CO3
• 2 nitrogen atoms
• 8 hydrogen atoms
• 1 carbon atom
• 3 oxygen atoms
• Moles of atoms in 1 mole of (NH4)2CO3
• Ex Ca(NO3)2

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Example

• Determine the mass of the following
• NaCl
• O2
• C
• CO2
• (NH4)3PO4

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• Given
• Wanted
• Units given X units wanted
• units given
• The only instance where you can have different
  compounds is when you have mol/ mol. Otherwise,
  you must have the same compound and always 1 mole.

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• How many carbon dioxide molecules are in 2.0
  moles of carbon dioxide?
• G
• W

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• A bottle of sodium nitrate contains 100.0 g of
  the compound, how many moles of sodium nitrate
  does it contain?
• What is the mass of 3.20 moles of zinc nitrate?

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• How many moles of carbon atoms are in 1.50 moles
  aspirin, C9H8O4? (13.5 moles)
• How many moles of aspirin contain 0.480 mol O
  atoms?

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• Calculate the number of nitrogen atoms in 35 g of
  NH4NO3.
• How many H atoms are in 1000 g of water?
• How many liters of H2 gas does 35 g of H2 gas
  contain?

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Stoichiometry

• Calculation of quantities in chemical equation
• Coefficients indicate number of particles and
  moles of each substance but not the actual number
  of grams or liters of that substance
• Need a Balanced Chemical Equation
• Whenever your given and wanted compounds are
  DIFFERENT, you must always go through mol/ mol.
  Then you look at the coefficients of a balanced
  chemical equation to determine the number of
  moles.

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• The coefficients in a chemical equation give us
  the conversion factors to get from the number of
  particles of one substance, grouped into moles,
  to the number of particles of another substance
  in a chemical change.
• A2 3 B2 ? 2 AB3
• Possible conversion factors are

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• N2 3H2 ? 2 NH3
• How many moles of NH3 are produced when 0.60 mol
  of nitrogen react with hydrogen?
• How many moles of hydrogen need to react in order
  to produce 2.5 moles of NH3?

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• Find the mass of Al required to produce 1.32 L of
  hydrogen gas _at_ STP from the following balanced
  reaction
• 2 Al 3 H2SO 4? Al2 (SO4)3 3 H2

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• How many moles of oxygen are needed to burn 0.52
  mol of Mg?
• 2 Mg O2 ? 2 MgO
• How many grams of Mg are needed to produce 25 g
  of MgO?