chapter 12 chemical reactions - bakersfield college science b12_handouts... · chapter 12 chemical...

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Chapter 12 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

•12-8. Liquid Fuels

•12-9. Gas Fuels

•12-10. Solid Fuels

•12-11. Temperature

•12-12. Other Factors

•12-13. Chemical Equilibrium

•12-14. Altering an Equilibrium

•12-15. Electrolysis

•12-16. Electrochemical Cells

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12-1. Phlogiston

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

Johann Becher 1635-1682)

Georg Stahl(1669-1734)

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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)

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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)

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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.

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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.

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Fig. 12.6

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12.3 The Mole Figs. 12.7-8

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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.

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Fig. 12.9

C3H8 + 5O2 ���� 3CO2 + 4H2O

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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.

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Fig. 12.10-11

35/97 people died in 1937

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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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Table 12.1

Histamine attacks

are greater when you

are hot. Cooling

down affected areas

can reduce allergy

symptoms.

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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.

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What makes Switzerland unique?

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Activation Energy

Chemical Reactions must go over an energy

hill like a mountain (Swiss Alps).

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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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Use of Various Fuels

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Liquid Fuels

Petroleum, a mixture of various hydrocarbons, is the source of most liquid fuels.

Use a catalytic converter to convert the polluting exhaust gases of burned lead-free gasoline into harmless gases.

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Gas Fuels

Natural gas is largely methane, CH4.

Syngas

Coal can be gasified

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Hydroelectric Energy

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Solid Fuels

Types of solid fuels include coal, wood, and coke

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Solid Fuels

Acid rain from sulfur impurities in coal.

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Chemical EquilibriumChemical EquilibriumChemical EquilibriumChemical 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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Electrolysis (Electroplating)Electrolysis (Electroplating)Electrolysis (Electroplating)Electrolysis (Electroplating)

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

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More examples of

electroplating.

Electrolysis (Electroplating)Electrolysis (Electroplating)Electrolysis (Electroplating)Electrolysis (Electroplating)

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Types of Batteries

The Lead Storage

BatteryElectrochemical cells use oxidation-

reduction reactions

to produce electric current.

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Types of Batteries

The

Alkaline

Battery

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Types of

Batteries

The

Lithium

Battery

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

Hydrogen Fuel Cell

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Lecture Quiz 12

1. How many atoms are in a mole?

2. What is activation energy?

3. Give an example of an exothermic reaction?

4. What is probably the cheapest form of energy?

5. How much does one mole of H2O weigh?

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Lecture Quiz 12

1. How many atoms are in a mole? 6.02x10-23

2. What is activation energy? Energy needed to get over the energy hill or cause a reaction.

3. Give an example of an exothermic reaction? Burning wood

4. What is probably the cheapest form of energy? Hydroelectric

5. How much does one mole of H2O weigh? 18g

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Lecture Quiz 12

1. What is a catalytic converter?

2. Who did an experiment with tin and light?

3. What does exothermic and endothermic mean?

4. Who discovered oxygen?

5. How much does one mole of CO2

weigh?

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Lecture Quiz 12

1. What is a catalytic converter?Found on exhaust pipe and converts pollutants to harmless gases.

2. Who did an experiment with tin and light? Antoine Lavoisier

3. What does exothermic and endothermic mean? exothermic-gives off heat, endothermic-absorbs heat

4. Who discovered oxygen? Joseph Pieistley

5. How much does one mole of CO2weigh? 44 grams (12 for carbon and 2x16 for oxygen)