Chemical Reactions

1
Chemical Reactions
2
Reactions

• Reactants ? Products
• Symbols
• (s) solid or insoluble
• (l) liquid
• (g) gas
• (aq) aqueous or soluble

3
Formula Weight

• The sum of the atomic weights (rounded to the
  nearest tenth) of all the atoms in a chemical
  formula
• CH4 1(12.0) 4(1.0) 16.0 amu
• 1 amu 1.66 x 10-24 gram

4
The Mole

• Nails and the hardware store
• Atoms and the chemical formula
• Atoms react in numbers
• Moles allow chemists to count atoms by weighing
  them

5
Amadeo Avogadro (1776-1856)

• Avogadro's number 6.02 x 1023
• 1 mole of atoms 6.02 x 1023 atoms
• 1 mole of molecules 6.02 x 1023 molecules

6
Using Avogadro's Number

• One hydrogen atom 1.0 amu
• One mole of H atoms 1.0 grams
• One carbon atom 12.0 amu
• One mole of C atoms 12.0 grams
• One molecule of CH4 16.0 amu
• One mole of CH4 16.0 grams

7
Grams to Moles Moles to Grams

• Atomic weight is a conversion factor
• One mole of CH4 16.0 grams
• 32 g CH4 x 1 mol/16.0 g 2.0 mol CH4

8

• 0.84 mol C3H8O X 60.0 g C3H8O/mol
• 50 g C3H8O
• Other problems from end of chapter.

9
Equations

• In order to use an equation in calculations, it
  must be balanced.
• There must be an equal number of atoms of each
  type on both sides of the arrow.
• H2 O2 ? H2O
• Hydrogen and oxygen are diatomic gases and always
  appear this way as elements.

10

• Since there are two oxygens on the left side, we
  need to have two on the right side.
• By placing a "2" in front of the H2O we have 2
  O's on the right side.
• We now have four hydrogens on the right.
• Placing a 2 in front of the H2 make four.
• 2H2 O2 ? 2H2O

11

• H2 N2 ? NH3
• Hydrocarbon combustion
• C3H8 O2 ? CO2 H2O
• C4H10 O2 ? CO2 H2O

12
Stoichiometry

• Predicting how much of a substance will react
  with another substance in a balanced chemical
  reaction.
• Predicting how much product can be formed from a
  given amount of reactants in a balanced chemical
  reaction.

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Mol Ratio

• The relationship between any two members of a
  chemical equation.
• N2 3H2 ? 2NH3
• 1 mol N2 / 3 mol H2
• 1 mol N2 / 2 mol NH3
• 3 mol H2 / 2 mol NH3

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Examples

• How many moles of NH3 can be produced from 2.0
  moles of N2?

15

• How many moles of NH3 can be produced from 56
  grams of N2?

16

• How many grams of NH3 can be produced from 56
  grams of N2?

17
Heat of Reaction

• Heat energy (calories) is either given off (an
  exothermic reaction) or taken in (an endothermic
  reaction).
• The Heat of Reaction is used to supply energy to
  living things so that physiological processes can
  take place.
• The combustion of carbohydrates is essential to
  our lives.

18

• When glucose is burned, 670 kcal is released per
  mole of glucose.
• How many kcal are produced when 15.0 g are burned?

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Types of Reactions
0

• Exchange Reactions
• Precipitation reactions
• Neutralization reactions
• Gas Formation reactions
• Oxidation-Reduction Reactions
• One substance is oxidized
• One substance is reduced

20
Types of Reactions
0

• Exchange Reactions
• Precipitation reactions
• Neutralization reactions
• Gas Formation reactions
• Oxidation-Reduction Reactions
• One substance is oxidized
• One substance is reduced

21
Ions in Solution
0

• When an ionic substance dissolves in water its
  ion components are dissociated
• NaCl ? Na Cl-
• MgCl2 ? Mg2 2Cl-
• NaHCO3 ? Na HCO3-

22
0

• Sometimes the ionic substance is insoluble and
  does not dissolve
• AgCl(s) ? NR
• BaSO4(s) ? NR

23
State Designations
0

• (s) solid or insoluble
• (l) liquid
• (g) gas
• (aq) soluble

24
Precipitation Reactions
0

• An insoluble substance is formed when two soluble
  substances are mixed.
• AgNO3(aq) NaCl(aq) ? AgCl(s) NaNO3(aq)
• The silver chloride precipitates and causes the
  reaction.

25
Spectator Ions
0

• Looking at the ions involved in the reaction
• Ag NO3- Na Cl- ?
• AgCl(s) Na NO3-
• Na and NO3- do nothing in the reaction, they
  are spectator ions.

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Net Ionic Equation
0

• Ag Cl- ? AgCl(s)
• Any source of silver ions and chloride ions would
  result in the same net ionic equation. Sodium
  chloride substitutes contain potassium chloride.

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Predicting Solubility
0

• Use of the Solubility Table (p. 106-107)
• Always soluble ions
• NH4 Na K NO3- CH3COO-

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0

• Which are soluble?
• Ca(NO3)2
• (NH4)3PO4
• Pb(NO3)2

29
0

• Even large biomolecules are made soluble by
  reaction with soluble ions
• Sodium benzoate mold retardant
• Sodium ascorbate soluble Vitamin C
• Sodium dodecylsulfate - detergent
• Be aware of surprise sources of sodium for high
  blood pressure patients.

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0

• Sodium chloride silver nitrate

31
0

• Copper(II) chloride sodium sulfide

32
0

• Calcium chloride sodium carbonate

33
0

• Barium nitrate sodium phosphate

34
0

• Chromium(III) chloride silver nitrate

35
Types of Reactions
0

• Exchange Reactions
• Precipitation reactions
• Neutralization reactions
• Gas Formation reactions
• Oxidation-Reduction Reactions
• One substance is oxidized
• One substance is reduced

36
Neutralization Reactions
0

• Acid Base ? Ionic substance H2O(l)
• HCl NaOH ? NaCl H2O(l)
• H OH- ? H2O(l)
• More in Chapter 8

37
Gas Formation Reactions
0

• 2H CO32- ? H2O(l) CO2(g)
• H HCO3- ? H2O(l) CO2(g)

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Examples

• Na2CO3 2HCl ?
• 2NaCl H2O(l) CO2(g)
• NaHCO3 HCl ?
• NaCl H2O(l) CO2(g)

39
Oxidation-Reduction Reactions

• Elements have different abilities to gain or lose
  electrons.
• We can harness this energy by putting two
  elements in a system and collecting the electrons
  as they move in the favored direction.
  (Batteries)

40
Assigning Oxidation Numbers

• Monatomic ions have an oxidation number the same
  as the charge
• Elements have an oxidation number of zero
• The members of compounds have oxidation numbers
  that add to zero (H will be H and O will be
  O2-)
• The members of polyatomic ions have oxidation
  numbers that add to the charge on the ion

41
Definitions

• Oxidation
• Loss of electrons
• Increase in oxidation number
• Reduction
• Gain of electrons
• Decrease in oxidation number

42

• Cu2 Zn(s) ? Cu(s) Zn2
• Cu2 gains 2 electrons reduced
• Zn(s) loses 2 electrons oxidized
• LEO GER

43

• Cu2 is reduced and is the OXIDIZING agent
• Zn(s) is oxidized and is the REDUCING agent

44
Organic Redox Reactions

• CH3CH2OH ? CH3CHO ? CH3COOH
• Ethyl alcohol ?acetaldehyde ?acetic acid
• C2H6O ? C2H4O ? C2H4O2