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Chemical equation & reactions



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  • 2. PREVIOUS NEXT CHEMICAL REACTIONS You should be able to Classify reactions by type. Write a balanced molecular equation, complete ionic equation, and a net ionic equation. Balance oxidation-reduction reactions. Predict if a precipitate will form using the solubility rules. Predict products of reactions given the chemical names of the reactants.
  • 3. PREVIOUS NEXT Organize Your Thoughts Chemical reactions Chemical Chemical equations equations • Synthesis • Balancing equations • Decomposition • Single replacement • Predicting products • Double replacement from reactants • CombustionPackard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175
  • 4. PREVIOUS NEXT DESCRIBING A CHEMICAL REACTIONIndications of a Chemical Reaction – Evolution of heat, light, and/or sound – Production of a gas – Formation of a precipitate – Color change
  • 5. PREVIOUS NEXT SIGNS OF CHEMICAL REACTIONSThere are five main signs that indicate a chemical reaction has taken place: release inputchange in color change in odor production of new input or release difficult to reverse gases or vapor of energy
  • 6. PREVIOUS NEXT CHEMICAL EQUATIONS aluminum oxide product Depict the kind of reactants and products and their relative amounts in a reaction. 4 Al(s) + 3 O2(g) 2 Al2O3(s) The letters (s), (g), and (l) are the physical states of compounds. The numbers in the front are called stoichiometric coefficients.
  • 7. PREVIOUS NEXT Chemical Equations aluminum oxide sandpaper 4 Al(s) + 3 O2(g) 2 Al2O3(s) 4 g Al + 3 g O2 yield 2 g Al2O3 This equation means:4 Al atoms + 3 O2 molecules yield 2 molecules of Al2O3 or 4 Al moles + 3 O2 moles yield 2 moles of Al2O3 4 mol Al@27g/mol 3 mol O2@32g/mol 2 mol Al2O3@102g/mol 108 g + 96 g = 204 g
  • 8. PREVIOUS NEXT CHARACTERSTICS OF CHEMICAL EQUATION • The equation must represent known facts. • The equation must contain the correct formulas for the reactants and products. • The law of conservation of mass must be satisfied.
  • 9. PREVIOUS NEXT CHEMICAL EQUATIONS• Reactants – the substances that exist before a chemical change (or reaction) takes place.• Products – the new substance(s) that are formed during the chemical changes.• CHEMICAL EQUATION indicates the reactants and products of a reaction. REACTANTS  PRODUCTS
  • 10. PREVIOUS NEXT WORD EQUATIONS• A WORD EQUATION describes chemical change using the names of the reactants and products. Write the word equation for the reaction of methane gas with oxygen gas to form carbon dioxide and water. methane + oxygen carbon dioxide + water Reactant Product CH4 + 2 O2 CO2 + 2 H2O
  • 11. PREVIOUS NEXTUNBALANCED AND BALANCED EQUATIONS H Cl Cl H H Cl H Cl Cl Cl H Cl H H H2 + Cl2  HCl (unbalanced) H2 + Cl2  2 HCl (balanced) reactants products reactants products H 2 1 H 2 2 Cl 2 1 Cl 2 2
  • 12. PREVIOUS NEXT Visualizing a Chemical Reaction 2 Na + Cl2 2 NaCl 10___ mole Na 5 ___ mole Cl2 1___ mole NaCl 10 ? 0
  • 13. PREVIOUS NEXT Types of Chemical Reactions Synthesis (Combination) reaction A + B  AB Decomposition reaction AB  A + B ASingle-replacement reaction A + compound compound +element element BC AC B BDouble-replacement reaction AB + CD  AD + CB compound compound compound compound Neutralization reaction HX + BOH  BX + HOH acid base salt water Combustion reaction (of a hydrocarbon) CH + O2  CO2 + H2O Polymerization Polymer = monomer + monomer + … Ause activity series to predict Bdriving force…water, gas, or precipitate
  • 14. PREVIOUS NEXT Summary of Classes of Reactions Chemical reactions Precipitation Oxidation-Reduction Acid-Base reactions Reactions Reactions Synthesis Decomposition Combustion reactions reactions Reactions (Reactants are (Products are elements.) elements.)
  • 15. PREVIOUS NEXT Summary of Classes of Reactions Chemical reactions Precipitation Oxidation-Reduction Acid-Base reactions Reactions Reactions Combustion Synthesis Decomposition Reactions reactions reactions
  • 16. PREVIOUS NEXT Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Cl2  2 NaCl Na Cl  Cl Na General form: A + B  AB element or element or compound compound
  • 17. PREVIOUS NEXT Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Cl2  2 NaCl Na Cl Na+ Cl - Cl Cl - Na+ Na General form: A + B  AB element or element or compound compound
  • 18. PREVIOUS NEXT Decomposition Reaction Decomposition reaction 2 H 2O 2 H2 + O2 H O H + H O H General form: AB A + B compound two or more elements or compounds
  • 19. Single and Double Replacement Reactions Single-replacement reaction Mg + CuSO4  MgSO4 + Cu General form: A + BC  AC + B Double-replacement reaction CaCO3 + 2 HCl  CaCl2 + H2CO3 General form:PREVIOUS AB + CD  AD + CB NEXT
  • 20. PREVIOUS NEXT Double Replacement Reaction K2CO3 (aq) + BaCl2 (aq) 2 KCl (aq) + BaCO3 (s) Potassium carbonate Barium chloride Potassium chloride Barium carbonate
  • 21. PREVIOUS NEXT Single-Replacement Reactions “Magic blue-earth” Fe + CuCl2 FeCl2 + Cu Can Fe replace Cu? Yes Zinc in nitric acid Zn + 2 HNO3 Zn(NO3)2 + H2 Can Zn replace H? Yes NO REACTION MgCl2 + Br2 MgBr2 + Cl2 Can Br replace Cl? No General Form A + BC AC + B
  • 22. PREVIOUS NEXT OXIDATION & REDUCTIONOxidation, in its original sense, refers to the combination of oxygen with another substance to produce a compound called an oxide. Iron, in the presence of water,combines with atmospheric oxygen to form a hydrated iron oxide, commonly called rust. Oxidation-reduction reactions combine a chemical wanting to gain electrons with a chemical willing to give up electrons. Such a reaction may be generally represented as follows: X·+ Y ⇄ XY· (where · represents an electron). The material that loses electrons is said to be oxidized and is called a reducing agent; the material that gains electrons is reduced and is called an oxidizing agent (see Chemical Reaction). The most common examples of oxidation are those reactions involving the combination of materials with the element oxygen, such as the rusting of iron or the burning of any combustible material in air. The equation for the burning of magnesium is: 2Mg(s) + O2(g) → 2MgO(s). When magnesium reacts with oxygen, each magnesium atom gives two electrons to oxygen. The positive magnesium ions (Mg 2+) then combine with negative oxygen ions (O2-) to form solid magnesium oxide (MgO). In this reaction, magnesium (the reducing agent) is oxidized, and oxygen (the oxidizing agent) is reduced. The reaction between metallic sodium and chlorine gas is an oxidation-reduction reaction that does not involve oxygen: This way of writing the oxidation-reduction reaction illustrates that both elements attain a noble-gas configuration (completely filled outer shells). Sodium loses an electron, achieving the noble gas configuration of neon, and chlorine gains an electron, achieving the noble gas configuration of argon.
  • 23. PREVIOUS NEXT CORROSIONCorrosion, partial or complete wearing away, dissolving, or softening of any substance by chemical or electrochemical reaction with its environment. The term corrosion specificallyapplies to the gradual action of natural agents, such as air or salt water, on metals.The most familiar example of corrosion is the rusting of iron, a complex chemical reaction in which the iron combines with both oxygen and water to form hydrated iron oxide. The oxide isa solid that retains the same general form as the metal from which it is formed but, porous and somewhat bulkier, is relatively weak and brittle.Three methods may be used to prevent the rusting of iron: (1) alloying the iron so that it will be chemically resistant to corrosion; (2) coating it with a material that will react with thecorroding substances more readily than the iron does and thus, while being consumed, protect the iron; and (3) covering it with an impermeable surface coating so that air and watercannot reach it. The alloying method is the most satisfactory but the most expensive. A good example is stainless steel, in which chromium or chromium and nickel are alloyed with theiron; this alloy is not only absolutely rustproof but will even resist the action of such corrosive chemicals as hot, concentrated nitric acid. The second method, protection with an activemetal, is also satisfactory, but expensive. The most common example of this method is galvanizing, in which iron is covered with zinc. In the presence of corrosive solutions, an electricpotential is set up between the iron and the zinc, causing the zinc to dissolve but protecting the iron as long as any zinc remains. The third method, protection by coating the surface withan impermeable layer, is the least expensive and therefore the most common. It is satisfactory as long as no crack appears in the coating. Once the coating cracks, however, rustingproceeds at least as fast as it would have with no protection. If the protective layer is an inactive metal, such as tin or chromium, an electric potential is set up, protecting the layer butacting on the iron and causing the rusting to proceed at an accelerated rate. The most satisfactory coatings are baked enamels; the least expensive are such paints as red lead.Some metals, such as aluminium, although very active chemically, appear not to corrode under normal atmospheric conditions. Actually, aluminium corrodes rapidly, and a thin,continuous, transparent layer of oxide forms on the surface of the metal, protecting it from further rapid corrosion. Lead and zinc, although less active than aluminium, are protected bysimilar oxide films. Copper, a comparatively inactive metal, is slowly corroded by air and water in the presence of such weak acids as carbonic acid, producing a green, porous, basiccarbonate of copper. Green corrosion products, called verdures or patina, appear on such copper alloys as brass and bronze, as well as on pure copper.Some metals, called noble metals, are so inactive chemically that they do not suffer corrosion from the atmosphere; among them are silver, gold, and platinum. A combination of air,water, and hydrogen sulphide will act on silver, but the amount of hydrogen sulphide normally present in the atmosphere is so small that the degree of corrosion is negligible except forthe black discoloration, called tarnishing, produced by the formation of silver sulphide.The corrosion of metals is more of a problem than that of other materials. Glass is corroded by strongly alkaline solutions and concrete by sulphate-bearing waters. The corrosionresistance of glass and concrete can be greatly increased by changes in their composition.
  • 24. PREVIOUS NEXT RANCIDITYRancidity is the chemical decomposition of fats, oils and other lipids. There are three basic types of rancidity. Hydrolytic rancidity occurs when water splitsfatty acid chains away from the glycerol backbone in glycerines. Oxidative rancidity occurs when the double bonds of an unsaturated fatty acid reactchemically with oxygen. Microbial rancidity refers to a process in which microorganisms such as bacteria use their enzymes, including lipases, to break downchemical structures in the fat. In each case, these chemical reactions result in undesirable doors and flavours. Rancidity refers to the spoilage of a food in such a way that it becomes undesirable (and usually unsafe) for consumption. When people say that a food has "gone bad," what they re usually talking about is rancidity. Most of the time, but not always, rancidity can change the doors or flavours of a food in such a way that it becomes very unpleasant to smell or taste.
  • 25. PREVIOUS