12-1. Phlogiston. Chapter 12 Chemical Reactions The Mole 4/7/2011. Fig

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1 Chapter 12 Chemical Reactions Phlogiston Oxygen The Mole Formula Units Exothermic and Endothermic Reactions Chemical Energy and Stability Activation Energy Liquid Fuels Gas Fuels Solid Fuels Temperature Other Factors Chemical Equilibrium Altering an Equilibrium Electrolysis Electrochemical Cells The English chemist Joseph Priestley discovered a gas that Lavoisier later named oxygen Joseph Priestley ( ) When oxygen combines chemically with another substance, the process is called oxidation, and the substance is said to be oxidized Phlogiston Fig Two early German chemists, Johann Becher and Georg Stahl, developed the phlogiston hypothesis. Johann Becher ) Georg Stahl ( ) 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. Rust is caused by the reaction of oxygen with iron. 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 The Mole The mole is a number, 6.02 x When you have a mole of something you have 6.02 x 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 6.02x10 23 atoms of carbon or 12.04x10 23 carbon atoms. Antoine Lavoisier ( ) 1

2 Fig Fig C 3 H 8 + 5O 2 3CO 2 + 4H 2 O 12.3 The Mole Figs Exothermic and Endothermic Reactions Chemical changes that give off energy are called exothermic reactions. Chemical changes that absorb energy are called endothermic reactions Formula Units Fig 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 = 40 grams. How much does a mole of H 2 O weigh? Add 2 times 1 for H and 16 for O to get 18 grams. How much does a mole of C 3 H 8 weigh? (3 x 12) + (8 x 1 ) = = 44 grams. 35/97 people died in

3 12.6 Chemical Energy and Stability What makes Switzerland unique? 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. Table 12.1 Histamine attacks are greater when you are hot. Cooling down affected areas can reduce allergy symptoms. What Affects Chemical Reactions? Temperature A 10 o C rise in temperature approximately doubles the speed of a chemical reaction occurring at or near room temperature. Concentration and Surface Area Activation Energy Chemical Reactions must go over an energy hill like a mountain (Swiss Alps). Catalysts (enzymes) A catalyst is a substance that can change the rate of a chemical reaction without itself being permanently changed. 3

4 O-zone depletion from Antarctica Gas Fuels 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 Syngas Natural gas is largely methane, CH 4. Coal can be gasified Use of Various Fuels Hydroelectric Energy Liquid Fuels Petroleum, a mixture of various hydrocarbons, is the source of most liquid fuels. Solid Fuels Types of solid fuels include coal, wood, and coke Use a catalytic converter to convert the polluting exhaust gases of burned lead-free gasoline into harmless gases. 4

5 Solid Fuels Acid rain from sulfur impurities in coal. Electrolysis (Electroplating) More examples of electroplating. Chemical Equilibrium Types of Batteries 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 CO 2 gas is in equilibrium with the water in the soda. Electrochemical cells use oxidationreduction reactions to produce electric current. The Lead Storage Battery Electrolysis (Electroplating) Types of Batteries The Alkaline Battery Steel plated with tin prevents corrosion and is used in beverage containers. One key above has been plated with copper. 5

6 Types of Batteries The Lithium Battery Hydrogen Fuel Cell Hydrogen gas is an excellent fuel produced by the electrolysis of water. 6

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