Chapter 10

Chemical Reactions

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For Science Fair JudgesRevised instructions!

Submit a list of projects that you judged with the associated grade-levels. A brief description of your impression of the projects would be helpful. (Be in SUB Ballroom by 5:00 PM for dinner and instructions.)

If you are not a judge, you may attend the Science Expo and write a detailed summary of at least two projects.

Either is extra-credit points or a lab make-up.

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Types of Chemical ReactionsTypes of Chemical Reactions

1) Oxidation-Reduction (Redox)

2) Combination

3) Decomposition

4) Replacement

5) Ion Exchange

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Oxidation-Reduction Reactions

(electron transfer reactions)

2 Mg (s) + O2 (g) 2 MgO (s)

Mg is the reducing agent (supplies electrons andis oxidized)

O2 is the oxidizing agent (takes electrons andis reduced)

Oxidation – an atom loses electrons

Reduction – an atom gains electrons

Mg2+O2-

Fig. 10.9 Example of an oxidizing agent (“chlorine”)

Others:

1) Bleach

2) Hydrogen

peroxide

3) Oxygen

4) Ultraviolet

light

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Types of Chemical ReactionsTypes of Chemical Reactions

1) Oxidation-Reduction (Redox)

2) Combination

3) Decomposition

4) Replacement

5) Ion Exchange

Fig. 10.10 Iron combines with oxygen to Fig. 10.10 Iron combines with oxygen to form rust (iron oxide)form rust (iron oxide)

4 Fe (s) + 3 O2 (g) 2 Fe2O3 (s)

Hydrogen combines with oxygenHydrogen combines with oxygento form water (dihydrogen monoxide)to form water (dihydrogen monoxide)

          

      

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Types of Chemical ReactionsTypes of Chemical Reactions

1) Oxidation-Reduction (Redox)

2) Combination

3) Decomposition

4) Replacement

5) Ion Exchange

Fig. 10.11 Decomposition of Mercury Oxide

2 HgO (s) → 2 Hg (l) + O2 (g)heat

1111

Decomposition of Hydrogen Peroxide

2 H2O2 (l) → 2 H2O (l) + O2 (g)

(Demo)

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Types of Chemical ReactionsTypes of Chemical Reactions

1) Oxidation-Reduction (Redox)

2) Combination

3) Decomposition

4) Replacement

5) Ion Exchange

Fig. 10.13 Replacement reaction between aluminum metal and the blue copper chloride solution

2 Al (s) 3 CuCl2 (aq) → 2 AlCl3 (aq) + 3 Cu (s)

CuCl2

CuAl

AlCl3

1414

• Replacement reactions take place when a Replacement reactions take place when a more active metal gives up electrons to a more active metal gives up electrons to a less active metal.less active metal.

• How do we know if a replacement reaction How do we know if a replacement reaction will take place or not occur?will take place or not occur?

• Refer to Refer to the activity seriesthe activity series

• Fig 10.12, p 264Fig 10.12, p 264

Fig. 10.12 The activity series for common metals

2 Na + 2H2O 2NaOH + H2 ↑

Zn + 2HCl ZnCl2 + H2 ↑

(Demo)

(Demo)

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Types of Chemical ReactionsTypes of Chemical Reactions

1) Oxidation-Reduction (Redox)

2) Combination

3) Decomposition

4) Replacement

5) Ion Exchange

2 KI + Pb(NO3)2 → PbI2 ↓ + 2 KNO3

PbI2

Pg 253

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Ion Exchange Reaction – ions of one compound

react with ions of another compound to form:

(1) a solid (precipitate) or

FeCl3 + 3 NaOH → Fe(OH)3 + 3 NaCl

(2) a gas or (3) water

CaCO3 + 2 HCl → CaCl2 + CO2 ↑ + H2O

By definition: 1 atom 12C “weighs” 12 u

On this scale

1H = 1.008 u

16O = 16.00 u

Atomic mass is the mass of an atom in atomic mass units (u)

Micro Worldatoms & molecules

Macro Worldgrams

Natural lithium is:

7.42% 6Li (6.015 u)

92.58% 7Li (7.016 u)

(7.42 · 6.015) + (92.58 · 7.016)100 = 6.941 u

Average atomic mass of lithium:

Average atomic mass (6.941)

mole - the amount of a substance that contains as many particles as there

are atoms in exactly 12.00 grams of 12C

1 mol = NA = 6.0221367 x 1023

Avogadro’s number (NA)

Molar mass - the mass of 1 mole of in gramseggsshoes

marblesatoms

1 mole 12C atoms = 6.022 x 1023 atoms = 12.00 g

1 12C atom = 12.00 u

1 mole 12C atoms = 12.00 g 12C

1 mole lithium atoms = 6.941 g of Li

For any element

atomic mass (u) = molar mass (grams)

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One Mole of:

C S

Cu Fe

Hg

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Molecular mass (or molecular weight) - the sum ofthe atomic masses (in u) in a molecule.

SO2

1S 32.07 u

2O + 2 x 16.00 u SO2 64.07 u

For any molecule

molecular mass (u) = molar mass (grams)

1 molecule SO2 = 64.07 u

1 mole SO2 = 64.07 g SO2