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Chemical Reactions 6.1 Types of Reactions (slides 2-14)
6.2 Factors Affecting Rates of Reactions (slides 16-32)
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6.1 Types of Chemical Reactions
HCl (aq) + NaOH (aq) H2O + NaCl
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Chemical Reactions HCl (aq) + NaOH (aq) H2O + NaCl
Acid Base Neutralization
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Chapter 6: Chemical Reactions Occur in Predictable Ways
Science 10 Chemistry Unit p
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6 Types of Chemical Reactions
Synthesis Decomposition Single Replacement Double Replacement Neutralization (Acid-Base) Combustion
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Why Study Chemical Reactions?
Studying different types of chemical reactions and factors that affect their rates, allows us to make predictions how other compounds will react with each other, their rates of reactions and the products that would form.
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1. Synthesis Reactions Two or more simple reactants combine to form a compound: A + B AB Synthesis of Ammonia: 3 H2(g) + N2(g) → 2 NH3(g) 2K + Cl2 2KCl CaO + CO2 CaCO3 2N2 + O2 2N2O
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2. Decomposition Opposite of synthesis reactions: a compound breaks down into two or more products (often elements). MgCl2 ---> Mg + Cl2 FeS ---> Fe + S Ba(ClO3)2 ---> BaCl2 + O2 Na2CO3 ---> Na2O + CO2 Ca(OH)2 ---> CaO + H2O
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3. Single Replacement Reaction
A reactive element (metal or non-metal) replaces an element in the compound it is reacting with to produce a new compound and element. Cu + AgNO3 ---> Ag + Cu(NO3)2 Fe + Cu(NO3)2 ---> Fe(NO3)2 + Cu Ca + H2O ---> Ca(OH)2 + H2 Zn + HCl ---> ZnCl2 + H2
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4. Double Replacement Reaction
Usually involves two ionic solutions that react to produce two other ionic compounds. One forms a precipitate, the other may form a ppt or remain in solution. Ionic soln + Ionic soln Ionic soln + ionic solid KOH + H2SO4 ---> K2SO4 + H2O FeS + HCl ---> FeCl2 + H2S NaCl + H2SO4 ---> Na2SO4 + HCl AgNO3 + NaCl ---> AgCl + NaNO3
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5. Neutralization Reactions
When acids and bases combine, they neutralize each other. They react to form a salt and water: Acid + base salt + water 2HCl2 + Ca(OH)2 CaCl2 + 2H2O H2SO4 + 2KOH K2SO4 + 2H2O HCl + NaOH NaCl + H2O
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6. Combustion Reactions Rapid reaction of oxygen with an compound containing carbon and hydrogen to produce CO2 and H2O. hydrocarbon + oxygen → carbon dioxide + water CH4 + O2 ---> CO2 + H2O C2H6 + O2 ---> CO2 + H2O C6H12O6 + O2 ---> CO2 + H2O C2H5OH + O2 ---> CO2 + H2O
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Summary of Chemical Reactions
1. Oxygen as one of its reactants and carbon dioxide and water as products: Combustion reaction 2. Two or more chemicals combining to form one chemical: Synthesis reaction 3. One large molecule falling apart to make several small ones: Decomposition reaction 4. Reaction has molecules that contain only one element: Single displacement reaction 5. Reaction has water as one of the products: Acid-base reaction 6. If none of these apply: Double displacement reaction
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Activity Create a skit demonstrating one of the six types of reactions
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6.2 Factors Affecting Rates of Reaction
Often, controlling the rate of a chemical reaction is as important as having the reaction occur in the first place. A bicycle chain will eventually rust if not protected but it happens very slowly See pages
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Reaction Rates The rate of reaction is how slowly or quickly reactants form the products A reaction that happens quickly has a high reaction rate. A reaction that takes a long time has a low reaction rate
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Temperature Temperature is a measure of the average energy of molecules. The more energy molecules have, the higher the temperature. When molecules have more energy, they move around more, bump into other molecules more, and therefore react faster. See page 275
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Temperature Cookies bake faster at higher temperatures.
Bread dough rises more quickly in a warm place than in a cool one. Low body temperatures slow down metabolism. In fact, warm-blooded animals regulate body temperature so that their biochemical reactions run at the correct rate. Lightsticks glow more intensely when dropped into hot water. Fridge slows down food spoilage.
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Changing the concentration of O2 changes the intensity of flames.
Concentration refers to how many molecules of a substance exist in a certain volume. How much solute (what’s dissolved) is there in a certain amount of solvent (what the substance is dissolved in. Concentration is measured in mass per unit volume (g/L). See page 275
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Concentration Usually, the higher the concentration of reactants, the faster the reaction occurs. Since there are more molecules per unit volume in high concentrations, there are more opportunities for molecules to collide and react. See page 275
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Concentration Eg. a splint of wood glows brighter in highly concentrated oxygen than in normal air, with a lower concentration of oxygen Two antacid tablets will neutralize a given amount of acid faster than one tablet will. Higher concentrations of acid in rain erode marble faster than lower concentrations. Fire extinguishers “remove” oxygen by smothering a fire, inhibiting combustion.
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Surface Area As more atoms are exposed to react,
more reactions take place See page 276
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Eg. A powdered substance has far more surface area than one, large chunk.
Eg. a powder only reacts more quickly if it is spread into the air instead of lying on a pan. Kindling vs log. Mythbusters coffee mate
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Surface Area Lakeland Sawmill explosion April 2012
The wood dust dispersed in the air was of sufficient concentration to explode. Friction in machinery gear generated frictional heat, providing ignition source for wood dust explosion. Two workers dead and 22 other workers injured, many seriously.
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Surface Area Coffee Mate contains Sodium Caseinate (C47H48N3O7S2Na) also known as casein. Sodium Caseinate contains the flammable element sulphur . When it is poured over a flame, individual particles ignite making the flame grow.
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Catalysts A catalyst speeds up a reaction without being used up in it.
Catalysts often lower the amount of energy necessary to break the bonds holding reactants together (activation energy). Sometimes increasing the temperature or concentration may be impractical or dangerous. See pages
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Salivary amylase increases the digestion of starches.
Catalysts Biological Catalysts: Enzymes are an example of biological catalysts Saliva has enzymes that help speed the breakdown of starches when they enter the mouth. Salivary amylase increases the digestion of starches.
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Catalysts Enzymes: Protease is used commercially to soften the meat.
Lactase to produce lactose-free milk. Enzymes in your body, such as maltase to hydrolyse starch / carbohydrate to maltose Beer and bread are typically made with yeast, a living organism containing enzymes.
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Catalysts Chlorine from CFCs acts as a catalyst to transform ozone (O3) in our atmosphere to elemental oxygen, which is not nearly as effective as ozone for shielding Earth from ultra-violet light. It is estimated that a single chlorine atom can destroy up to 1 million ozone molecules per second.
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Catalysts A catalytic converter is a device installed in all cars to decrease pollution. Car exhaust passes through the catalytic converter before leaving the car. A series of reactions involving catalysts, platinum, rhodium and palladium, convert toxic carbon monoxide into carbon dioxide. Poisonous nitrogen oxides are converted into nitrogen gas and oxygen gas. Take the Section 6.2 Quiz
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