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Chemical Equations & Reactions

Chemical Equations & Reactions

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Chemical Equations & Reactions

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  1. Chemical Equations & Reactions Chemistry A

  2. Chemical Reactions • You should be able to • Classify reactions by type. • Write a balanced molecular equation, complete ionic equation, and a net ionic equation. • Predict products of reactions given the chemical names of the reactants.

  3. Organize Your Thoughts Chemical reactions Chemical equations Chemical equations • Synthesis • Decomposition • Single replacement • Double replacement • Combustion • Balancing equations • Predicting products • from reactants Packard, Jacobs, Marshall, Chemistry Pearson AGS Globe, page 175

  4. Chemical Reaction A process in which at least one new substance is produced as a result of chemical change.

  5. A Chemical Reaction Reactants Products

  6. Describing a Chemical Reaction Indications of a Chemical Reaction • Evolution of heat, light, and/or sound • Production of a gas • Formation of a precipitate • Color change

  7. Signs of Chemical Reactions There are five main signs that indicate a chemical reaction has taken place: release input change in color change in odor production of new gases or vapor input or release of energy difficult to reverse

  8. Writing a Chemical Equation Chemical symbols give a “before-and-after” picture of a chemical reaction Reactants Products MgO + C CO + Mg magnesium oxide to form carbon monoxide reacts with carbon and magnesium

  9. Learning Check E3 12 oz of dough, 4 oz mushrooms, 12 slices pepperoni, 8 oz cheese and 5 oz tomato sauce are used to make a pizza. Write a recipe in words for putting together a pizza. How would you write the recipe as an equation?

  10. Solution E3 Example: Combine 12 oz dough + 4 oz mushrooms + 12 slices pepperoni + 8 oz cheese + 5 oz tomato sauce and heat 30 minutes at 350°C to produce 1 pizza 12 oz dough + 4 oz mshrm + 12 pep + 8 oz chse 1 pizza + 5 oz tom sauce

  11. 4 Al(s) + 3 O2(g) 2 Al2O3(s) Chemical Equations aluminum oxide product reactants Depict the kind of reactants and products and their relative amounts in a reaction. The letters (s), (g), and (l) are the physical states of compounds. The numbers in the front are called stoichiometric coefficients.

  12. 4 Al(s) + 3 O2(g) 2 Al2O3(s) Chemical Equations aluminum oxide sandpaper 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 O2moles yield 2 moles of Al2O3 2 mol Al2O3@102g/mol 4 mol Al@27g/mol 3 mol O2@32g/mol 108 g + 96 g = 204 g

  13. Chemical Equations Because the same atoms are present in a reaction at the beginning (reactants) and at the end (products), the amount of matter in a system does not change. The Law of Conservation of Matter 20% Chemical Factory 100% 100% 80% Kotz web

  14. Chemical Equations Because of the principle of the conservation of matter, An equation must be balanced. It must have the same number of atoms of the same kind on both sides. Lavoisier, 1788

  15. Characteristics of Chemical Equations • 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.

  16. 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

  17. 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. carbon dioxide + water methane + oxygen Reactant Product O2 2 H2O 2 CO2 CH4 + +

  18. Cl H H H Cl Cl Cl H reactants products reactants products H H Cl Cl Unbalanced and Balanced Equations H Cl Cl Cl H H H2 + Cl2 2 HCl (balanced) (unbalanced) H2 + Cl2 HCl 2 1 2 2 1 2 2 2

  19. Visualizing a Chemical Reaction 2 2 Na + Cl2 NaCl 10 5 10 10 ? 10 5 ___ mole Na ___ mole Cl2 ___ mole NaCl

  20. Visualizing a Chemical Reaction 2 2 Na + Cl2 NaCl

  21. Meaning of Chemical Formula Chemical Symbol Meaning Composition H2O One molecule of water: Two H atoms and one O atom 2 H2O Two molecules of water: Four H atoms and two O atoms H2O2 One molecule of hydrogen peroxide: Two H atoms and two O atoms

  22. Balancing Chemical Equations Balanced Equation – one in which the number of atoms of each element as a reactant is equal to the number of atoms of that element as a product What is the relationship between conservation of mass and the fact that a balanced equation will always have the same number of atoms of each element on both sides of an equation? Determine whether the following equation is balanced. 2 Na + H2O  2 NaOH + H2 2 Na + 2 H2O  2 NaOH + H2

  23. Balancing Chemical Equations • Write a word equation for the reaction. • Write the correct formulas for all reactants and products. • Determine the coefficients that make the equation balance.

  24. Balancing Chemical Equations Other examples NO(g) + O2(g)  NO2(g) • is it balanced? Is this balanced? • NO(g) + O(g)  NO2(g) Is this OK? • NO(g) + ½ O2(g)  NO2(g) Is this balanced? Is this OK?

  25. Balancing Chemical Equations An important point to remember • 2NO(g) + O2(g)  2NO2(g) • The 2 to the left of NO(g) and NO2(g) refers to the number of molecules present in the balanced equation. • It is a “multiplier” for every atom in the molecule. The subscript 2 in O2 (g) and NO2(g) refers to the number of atoms of this type that are present in each molecules (or ionic compound).

  26. Write a balanced equation for the reaction between chlorine and sodium bromide to produce bromine and sodium chloride. 1) Write a word equation for the reaction. chlorine + sodium bromide  bromine + sodium chloride 2) Write the correct formulas for all reactants and products. Cl2 + NaBr  Br2 + NaCl 3) Determine the coefficients that make the equation balance. Cl2 + 2 NaBr  Br2 + 2 NaCl

  27. Write the balanced equation for the reaction between aluminum sulfate and calcium chloride to form a white precipitate of calcium sulfate. 1) Write a word equation for the reaction. ? ? aluminum sulfate + calcium chloride  calcium sulfate + aluminum chloride 2) Write the correct formulas for all reactants and products. Al2(SO4)3 + CaCl2 CaSO4 + AlCl3 3) Determine the coefficients that make the equation balance. Al2(SO4)3 + 3 CaCl2 3 CaSO4 + 2 AlCl3

  28. CH4 + 2 O2 CO2 + 2 H2O Reactants Products 1 C atom 1 C atom 4 H atoms 4 H atoms 4 O atoms 4 O atoms

  29. Reactants  Products + C(s) + O2(g) CO2(g) carbon oxygen carbon dioxide Reactants Product 1 carbon atom 1 carbon atom 2 oxygen atoms 2 oxygen atoms catalyst – speeds up reaction + Pt 2 H2(g) + O2(g) H2O(l) hydrogen oxygen water 2 Pt Reactants Product 2 hydrogen atoms 2 hydrogen atoms 2 oxygen atoms 1 oxygen atoms Reactants Product 2 hydrogen atoms 4 hydrogen atoms 2 oxygen atoms 2 oxygen atoms Reactants Product 4 hydrogen atoms 4 hydrogen atoms 2 oxygen atoms 2 oxygen atoms Un balanced

  30. Showing Phases in Chemical Equations Solid Phase– the substance is relatively rigid and has a definite volume and shape. NaCl(s) Liquid Phase – the substance has a definite volume, but is able to change shape by flowing. H2O(l) Gaseous Phase – the substance has no definite volume or shape, and it shows little response to gravity. Cl2(g) H2O(s) H2O(l) H2O(g)

  31. Additional Symbols Used in Chemical Equations “Yields”; indicates result of reaction Used to indicate a reversible reaction A reactant or product in the solid state; also used to indicate a precipitate Alternative to (s), but used only to indicate a precipitate A reactant or product in the liquid state A reactant or product in an aqueous solution (dissolved in water) A reactant or product in the gaseous state (s) (l) (aq) (g)

  32. Additional Symbols Used in Chemical Equations Alternative to (g), but used only to indicate a gaseous product Reactants are heated Pressure at which reaction is carried out, in this case 2 atm Pressure at which reaction is carried out exceeds normal atmospheric pressure Temperature at which reaction is carried out, in this case 0 oC Formula of catalyst, in this case manganese (IV) oxide, used to alter the rate of the reaction D 2 atm pressure 0 oC MnO2

  33. Types of Chemical Reactions Synthesis (Combination) reaction A + B  AB Decomposition reaction AB  A + B ASingle-replacement reaction A + BC  AC + B element compound compound element BDouble-replacement reaction AB + CD  AD + CB compound compound compound compound HX + BOH  BX + HOH Neutralization reaction acid base salt water CH + O2 CO2 + H2O Combustion reaction (of a hydrocarbon) Polymer = monomer + monomer + … Polymerization Ause activity series to predict Bdriving force…water, gas, or precipitate

  34. Types of Chemical Reactions Synthesis (Combination) reaction A + B  AB Decomposition reaction AB  A + B ASingle-replacement reaction A + BC  AC + B BDouble-replacement reaction AB + CD  AD + CB HX + BOH  BX + HOH Neutralization reaction CH + O2 CO2 + H2O Combustion reaction (of a hydrocarbon) Polymer = monomer + monomer + … Polymerization Ause activity series to predict Bdriving force…water, gas, or precipitate

  35. Synthesis Reaction Direct combination reaction (Synthesis) 2 Na + Cl2 2 NaCl Na Na Cl Cl  Cl Cl Na Na General form: A + B  AB element or element or compound compound compound

  36. 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 compound

  37. H H H H Decomposition Reaction Decomposition reaction 2 H2O + 2 H2 O2 H O O H + H O O H General form: AB A + B compound two or more elements or compounds

  38. 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: AB + CD  AD + CB

  39. Double Replacement Reaction K2CO3 (aq) Potassium carbonate + BaCl2 (aq) Barium chloride 2 KCl (aq) Potassium chloride + BaCO3 (s) Barium carbonate

  40. CO2 + H2O C6H12O6 + O2 H2 + O2 H2O Na + Cl2NaCl A + B C Synthesis Reactions Photosynthesis 6 6 6 Formation of water 2 2 Formation of salt 2 2 General Form

  41. H2O2 H2O + O2 electricity H2O H2 +O2 NI3N2 + I2 AB A + B Decomposition Reactions Hydrogen Peroxide 2 2 Electrolysis of water 2 2 Nitrogen triiodide 2 3 General Form