Chapter 12a Chemical Reactions

•12-1. Phlogiston

•12-2. Oxygen

•12-3. The Mole

•12-4. Formula Units

•12-5. Exothermic and Endothermic Reactions

•12-6. Chemical Energy and Stability

•12-7. Activation Energy

12-1. Phlogiston

Two early German chemists, Johann Becher and Georg Stahl, developed the phlogiston hypothesis.

Johann Becher 1635-1682)

Georg Stahl(1669-1734)

The seventeenth century French chemist Antoine Lavoisier performed experiments that rejected the phlogiston hypothesis.

Lavoisier's experiments suggested that when tin is heated, the white powder formed results from the tin combining with a gas from the air. The increase in mass of the powder over the tin was the mass of the gas.

Lavoisier revolutionized chemistry by basing his ideas on accurate measurements.

Antoine Lavoisier

(1743-1794)

The English chemist Joseph Priestley discovered a gas that Lavoisier later named oxygen

When oxygen combines chemically with another substance, the process is called oxidation, and the substance is said to be oxidized.

Joseph Priestley(1733-1804)

Fig. 12.4-5

Rust is caused by the reaction of oxygen with iron.A fire can be put out by cooling it with water or

depriving it of oxygen. Burning is the result of oxygen reacting with other materials.

12.3 The Mole

The mole is a number, 6.02 x 1023. When you have a mole of something you have 6.02 x 1023 of them. When you have a mole of atoms or molecules you have enough to see and weigh. The weight of a mole of one type of atoms is the atomic weight from the periodic table in grams. The mole allows you to count atoms by weighing. For example, how many carbon atoms are there in 24 grams of carbon? From the periodic table each mole has 12 grams. So there are 2 moles or 2 x 6.02x1023 atoms of carbon or 12.04x1023 carbon atoms.

Fig. 12.6

12.3 The Mole Figs. 12.7-8

12.4 Formula Units

To find out how much a mole of molecules weigh you just add up the atomic weights of the atoms in the molecule.

How much does one mole of NaOH weigh?

Add the atomic weights of Na, O, and H you get 23 + 16 + 1 = 40 grams. How much does a mole of H2O weigh?

Add 2 times 1 for H and 16 for O to get 18 grams. How much does a mole of C3H8 weigh?

(3 x 12) + (8 x 1 ) = 36 + 8 = 44 grams.

Fig. 12.9C3H8 + 5O2 3CO2 + 4H2O

12.5 Exothermic and Endothermic Reactions

•Chemical changes that give off energy are called exothermic reactions.

•Chemical changes that absorb energy are called endothermic reactions.

Fig. 12.10-11

35/97 people died in 1937

12.6 Chemical Energy and Stability

The more energy needed to decompose a substance, the greater the chemical stability of the substance (with a few exceptions).

Chemical energy is electron potential energy.

When electrons move to new locations during an exothermic reaction, some of their original potential energy is liberated.

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Collision Model

• Molecules must collide in order for a reaction to occur.

• Rate depends on concentrations of reactants and temperature.

What makes Switzerland unique?

12.7 Activation Energy

Chemical Reactions must go over an energy hill like a mountain (Swiss Alps).

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Catalyst

• A substance that speeds up a reaction without being consumed or makes a tunnel through the Activation Energy Hill.

Chlorofluoro Carbons (CFC’s) are acting as catalysts to decompose the ozone (O3) layer. The ozone layer is formed from cosmic radiation and protects us from UV light.

O-zone depletion from Antarctica

Depletion is measured by T.O.M.S.

“Total O-zone Mapping Spectrometer”

The below dark shaded are shows the amount of depletion around the Antarctica

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An Amana refrigerator, one of many appliances that now use HFC-134a. This compound is replacing CFC’s, which lead to the destruction of atmospheric ozone.

Enzyme – catalyst in a biological system

Catalyst

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Use a catalytic converter to convert the polluting exhaust gases of burned lead-free gasoline into harmless gases. Platinum (Pt) is the catalysts used. Only a small amount is needed.

Chapter 12b Chemical Reactions

•12-8. Reaction Rates

•12-9. Other Factors

•12-10. Chemical Equilibrium

•12-11. Altering Chemical Equilibrium

•12-13. Electrochemical Cells

12-8 What Affects Chemical Reactions?

•Temperature•A 10oC rise in temperature approximately doubles the speed of a chemical reaction occurring at or near room temperature.

•Concentration and Surface Area

•Catalysts (enzymes)•A catalyst is a substance that can change the rate of a chemical reaction without itself being permanently changed.

Histamine attacks are greater when you are hot. Cooling down affected areas can reduce allergy symptoms.

12-8 What Affects Chemical Reactions?

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12-10 Chemical Equilibrium

• A dynamic state where the concentrations of all reactants and products remain constant.

12.10 Chemical Equilibrium

In a chemical equilibrium, forward and reverse reactions

occur at the same rate; the concentration of the reactants

and products remain constant. You can cause the equilibrium to shift by adding

or removing reactants or products.

Below CO2 gas is in equilibrium with the water in

the soda.

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Industrial Application-The Manufacture of Ammonia

N2(g) + 3H2(g) 2NH3(g) ΔH = -92.4 kJ mol-1

To increase production how would you manipulate the equilibrium?

2. Lower Temperature

1. Lower Volume

3. Remove Product

12-11 Altering Chemical Equilibrium

Electrolysis (Electroplating)

Steel plated with tin prevents corrosion and is used in beverage containers. One key above has been plated with copper.

More examples of

electroplating.

Electrolysis (Electroplating)

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• Oxidation–reduction reaction (redox reaction) – a chemical reaction involving the transfer of electrons. Oxidation – loss of electrons Reduction – gain of electrons

http://www.youtube.com/watch?v=Ftw7a5ccubs

Types of Batteries

The Lead Storage BatteryElectrochemical

cells use oxidation-reduction reactions to produce electric current.

Types of Batteries

The Alkaline Battery

Types of Batteries

The Lithium Battery

Hydrogen gas is an excellent fuel produced by the electrolysis of water.

Hydrogen Fuel Cell