Burns FUNDAMENTALS OF CHEMISTRY 4/e

1
Burns FUNDAMENTALS OF CHEMISTRY 4/e

• Chapter 10
• Chemical Reactions

2
Chemical Reactions

• Chemical reactions are chemical changes.
• Chemical reactions are represented by chemical
  equations.
• Much information about the qualitative and
  quantitative aspects of a reaction can be
  determined from the equations

3
Meaning of a Chemical Equation

• When nitrogen (from the air) is combined with
  hydrogen (from natural gas), ammonia is formed
• N2 H2 NH3
• This equation is not balanced. There need to be
  the same number of atoms of each type represented
  on the left of the arrow as there are on the
  right side of the arrow. Since the formulas of
  the compounds and elements have been specified,
  the subscripts cant be changed.

4
Reactants and Products

• The Reactants are the substances that are the
  starting materials. Their formulas are written
  on the left side of the arrow.
• The Products are the substances produced in a
  chemical reaction. Their formulas are written on
  the right side of the arrow.
• The arrow is interpreted as yields in an equation.

5
Balancing the Equation

• N2 H2 NH3
• Coefficients are used to balance the equation.
• There are two Ns on the left. To get 2 Ns on
  the right, place a coefficient of 2 in front of
  NH3
• N2 H2 2NH3
• Now there are two NH3 molecules, representing 2
  Ns and 2x3 6 Hs

6
N2 H2 2NH3

• To get 6 Hs on the left, place a coefficient of
  3 in front of H2
• N2 3H2 2NH3
• Now the equation is balanced
• atom L R
• N 1x22 2x12
• H 3x26 2x36

7
Balancing Atoms
Insert Figure 10.9
8
What does this equation mean?

• N2 3H2 2NH3

3 molecules of hydrogen (each containing 2 atoms)
to form
2 molecules of ammonia. ( Each molecule contains
1 atom of nitrogen and 3 atoms of hydrogen.)
1 molecule of nitrogen (each containing 2 atoms)
reacts with
3 moles of hydrogen (H2) to form
1 mole of nitrogen (N2) reacts with
2 moles of ammonia (NH3)
9
Quantitative Relationships

• N2 3H2 2NH3

3x(2x1) 6 g of H2 to form
1x(2x14) 28g of N2 reacts with
2x(143x1) 34 g of NH3.
Product 34 g
Reactants 26 6 34 g
These are mass ratios for reactants and
products N2 H2 NH3 28 6 34 14
3 17
10
Indicate the Physical State

• N2(g) 3H2(g)
  2NH3(g)

(g) gas (s) solid (l) liquid (aq) aqueous,
dissolved in water
11
Classification of Reactions

• Combustion
• Reaction of organic compounds with oxygen to form
  carbon dioxide and water.
• Combination (Synthesis)
• A B AB
• Decomposition
• AB A B
• Single Replacement
• A BC AC B
• Double Replacement
• AB CD AD CB

12
Combustion

• Organic compounds containing carbon and hydrogen
  are called hydrocarbons.
• Other organic compounds also contain oxygen.
• When these compounds burn, the reaction is said
  to be combustion.
• The products are carbon dioxide and water.
• CxHyOz O2 CO2 H2O
  (unbalanced)

13
Writing and Balancing Combustion Equations

• Write the equation, placing the organic compound
  and O2 to the left of the arrow as reactants.
  Place CO2 and H2O to the right of the arrow as
  products.
• 1. Balance the C atom first.
• 2. Balance the H atom second.
• 3. Balance the O atoms last.
• 4. Fractional coefficients may be needed for O2
• 5. If fractional coefficients are needed,
  multiply through by 2 to get integers.

14
An Example Combustion Reaction

• Write the balanced equation for the combustion of
  ethane, C2H6.
• Write the reactants and products
• C2H6 O2 CO2 H2O
• Balance the C
• C2H6 O2 2CO2 H2O
• Balance the H
• C2H6 O2 2CO2 3H2O

15
C2H6 O2 2CO2 3H2O

• Balance the O. There are 2x2 3 7 Os on the
  left. To balance the right you need 7/2 as a
  coefficient for O2
• C2H6 7/2O2 2CO2 3H2O
• Multiply the coefficients by 2
• 2C2H6 7O2 4CO2 6H2O

16
2C2H6 7O2 4CO2 6H2O

• Check

17
Synthesis Reactions(Producing Compounds From the
Elements

• Producing Ammonia (Haber Process)
• N2(g) 3H2(g) 2NH3(g)
• Producing water from the elements
• 2H2(g) O2(g) 2H2O(l)
• Rusting of iron
• 4Fe(s) 3O2(g) 2Fe2O3(s)

18
Decomposition ReactionsBreaking Compounds into
the Elements

• Electrolysis of water
• 2H2O(l) 2H2(g) O2(g)
• Decomposition of metal oxides
• 2HgO(s) 2Hg(l) O2(g)
• Decomposition of chlorates
• 2 KClO3(s) 2KCl(s) O2(g)

DC current
Heat
MnO2
heat
19
Decomposition of Water by Electrolysis
20
Decomposition Reactions

• Decomposition of Nitrates
• 2NaNO3 2NaNO2 O2
• Decomposition of Hydrogen Peroxide, H2O2
• 2H2O2 2H2O
  O2

heat
MnO2 or I-
21
Reactions of Metals

• Metal Oxygen Metal oxide
• 4Na(s) O2(g) 2Na2O(s)
• 2Mg(s) O2(g) MgO(s)
• Metal Oxides React with water
• Metal oxide water Metal hydroxide
• Na2O(s) H2O(l) 2NaOH(aq)
• MgO(s) H2O(l) Mg(OH)2(aq)

22
Reaction of Metals with Oxidizing Agents

• Cu(s) Cl2(g) CuCl2(s)
• This is an example of an oxidation-reduction
  reaction (REDOX)
• Copper is oxidized (electrons are lost)
• Cu Cu2 2e-
• Chlorine is reduced (electrons are gained)
• Cl2 2e- 2Cl-
• Overall Cu2 2Cl- CuCl2

23
Oxidation/Reduction

• Cu(s) Cl2(g) CuCl2(s)
• Cl2 causes Cu to be oxidized and is called the
  oxidizing agent.
• Cu causes Cl2 to be reduced and is the reducing
  agent.
• Cu(s) Cl2(g)
  CuCl2(s)
• red agent ox agent
• loses electrons gains electrons
• is oxidized is reduced

24
Single Replacement Reactions

• Cu(s)2AgNO3(aq) Cu(NO3)2(aq) 2Ag(s)
• Cu is oxidized to Cu2 ions
• Ag is reduced to Ag atoms
• Cu2 ions have replaced the Ag ions in AgNO3
• To determine which metals will replace which ions
  in aqueous solution, use the activity series.
• Elements toward the top of the series will
  replace elements below them. Cu is above Ag in
  the series.

25
A Short Activity Series
Li Li e- Na Na
2e- Mg Mg2 2 e- Zn
Zn2 2e- H2 2H
2e- Cu Cu2 2e- Ag
Ag e-
26
Reaction of Active Metals with Water

• Many of the active metals toward the top of the
  activity series will react with water or steam
• metal water metal hydroxide hydrogen
• 2 Na(s) 2H2O(l) 2NaOH(aq) H2(g)
• Ca(s) 2H2O(l) Ca(OH)2(aq) H2(g)

27
Reaction of Metals with Acid

• Metals above H2 in the activity series will react
  with acids to produce the metal salt and hydrogen
  gas
• metal acid salt hydrogen
• Zn(s) 2HCl(aq) ZnCl2(aq) H2(g)

28
Reactions of Non-metals

• Non-metals will react with oxygen to form
  non-metal oxides
• S8(s) 8O2(g) 8SO2(g)
• Non-metals will also react with Cl2 or Br2
• P4(s) 6Br2(l) 4PBr3(l)
• Non-metal oxides react with water to form acids
• SO2(g) H2O(l) H2SO3(aq) (sulfurous
  acid)

29
Single Displacement Reactions of Non-metals

• Halogens will displace halide ions.
• The activity series for halogens follows the
  periodic table F2 gt Cl2 gt Br2 gt I2.
• Cl2 comes before I2 and will displace I in
  compounds
• Cl2 2NaI I2 NaCl
• I2 will not displace Cl in compounds
• I2 NaCl N. R. (no reaction)

30
Double Displacement Reactions

• Two types of Double Displacement Reactions
• 1. Formation of an insoluble precipitate.
• 2. Formation of a gas.
• Gas Formation
• Acid salt gas another salt
• H2SO4(aq) Na2S(aq) H2S(g) Na2SO4(aq)
• 2HCl (aq) CaCO3(s) CO2(g) H2O(l)
  CaCl2(aq)

31
Precipitation Reactions

• A precipitation reaction occurs when two
  solutions of salts are mixed and an insoluble
  salt is formed. The insoluble salt, which
  separates from the solution is called a
  precipitate
• Pb(NO3)2(aq) 2KI(aq) PbI2(s) 2KNO3(aq)
• NaCl(aq) AgNO3(aq) NaNO3(aq) AgCl(s)

32
Ionic and Net Ionic Equations

• Since salts (ionic compounds) exist as ions in
  solution, a precipitation reaction can be shown
  as ions

NaCl(aq) AgNO3(aq) NaNO3(aq) AgCl(s)
Na(aq) Cl-(aq) Ag(aq) NO3-(aq)
Na(aq) NO3-(aq) AgCl(s)
This is the ionic equation for the reaction. Na
and NO3- ions are on both side, so they can be
cancelled
Cl-(aq) Ag(aq) AgCl(s)
This is called the net ionic equation. Na and
NO3- are spectator ions.
33
Neutralization Reactions

• Another type of double replacement reaction is
  the neutralization reaction, also called an
  acid-base reaction
• acid base salt water
• Acid-H containing compound.
• Base- OH- containing compound.
• Salt-Ionic compound containing the anion of the
  acid and the cation of the base.

34
Neutralization Reactions

• Acid base water salt

Overall reaction
HCl(aq) NaOH(aq) H2O(l) NaCl(aq)
Ionic Equation H Cl- Na OH-
H2O(l) Na Cl-
Cancel spectator ions to get net ionic equation
H(aq) OH-(aq) H2O(l)