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Chapter 7 Chemical Reactions

2. Experiencing Chemical Change. chemical reactions are happening both around you and in you all the timesome are very simple, others are complexin terms of the pieces ? even the simple ones have a lot of interesting principles to learn fromchemical reactions involve changes in the structures of the molecules, and many times we can experience the effects of those changesWhat are some examples of chemical reactions you experience?.

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Chapter 7 Chemical Reactions

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    1. Chapter 7 Chemical Reactions

    2. 2 Experiencing Chemical Change chemical reactions are happening both around you and in you all the time some are very simple, others are complex in terms of the pieces – even the simple ones have a lot of interesting principles to learn from chemical reactions involve changes in the structures of the molecules, and many times we can experience the effects of those changes What are some examples of chemical reactions you experience?

    3. 3 Chemical Reactions Reactions involve chemical changes in matter resulting in new substances Reactions involve rearrangement and exchange of atoms to produce new molecules Elements are not transmuted during a reaction

    4. 4 Evidence of Chemical Reactions look for evidence of a new substance visual clues (permanent) color change precipitate formation solid that forms when liquid solutions are mixed gas bubbles large energy changes container becomes very hot or cold emission of light other clues new odor whooshing sound from a tube permanent new state

    5. 5 Evidence of Chemical Change

    6. 6 Evidence of Chemical Change in order to be absolutely sure that a chemical reaction has taken place, you need to go down to the molecular level and analyze the structures of the molecules at the beginning and end

    7. 7 Chemical Equations Shorthand way of describing a reaction Provides information about the reaction Formulas of reactants and products States of reactants and products Relative numbers of reactant and product molecules that are required Can be used to determine weights of reactants used and products that can be made

    8. 8 Conservation of Mass Matter cannot be created or destroyed Therefore the total mass cannot change and the total mass of the reactants will be the same as the total mass of the products In a chemical reaction, all the atoms present at the beginning are still present at the end if all the atoms are still there, then the mass will not change

    9. 9 The Combustion of Methane methane gas burns to produce carbon dioxide gas and gaseous water whenever something burns it combines with O2(g)

    10. 10 Combustion of Methane methane gas burns to produce carbon dioxide gas and gaseous water whenever something burns it combines with O2(g) CH4(g) + O2(g) ® CO2(g) + H2O(g)

    11. 11 Combustion of Methane Balanced to show the reaction obeys the Law of Conservation of Mass it must be balanced CH4(g) + 2 O2(g) ® CO2(g) + 2 H2O(g)

    12. 12 Chemical Equations CH4 and O2 are the reactants, and CO2 and H2O are the products the (g) after the formulas tells us the state of the chemical the number in front of each substance tells us the numbers of those molecules in the reaction called the coefficients

    13. 13 Chemical Equations this equation is balanced, meaning that there are equal numbers of atoms of each element on the reactant and product sides to obtain the number of atoms of an element, multiply the subscript by the coefficient 1 ? C ? 1 4 ? H ? 4 4 ? O ? 2 + 2

    14. 14 Symbols Used in Equations symbols used to indicate state after chemical (g) = gas; (l) = liquid; (s) = solid (aq) = aqueous = dissolved in water energy symbols used above the arrow for decomposition reactions D = heat hn = light shock = mechanical elec = electrical

    15. 15 Writing Balanced Chemical Equations Write a skeletal equation by writing the formula of each reactant and product Count the number of atoms of each element on each side of the equation polyatomic ions may often be counted as if they are one “element” Pick an element to balance if an element is found in only one compound on both sides, balance it first leave elements that are free elements somewhere in the equation until last

    16. 16 Writing Balanced Chemical Equations Find the Least Common Multiple of the number of atoms on each side the LCM of 3 and 2 is 6 Multiply each count by a factor to make it equal to the LCM Use this factor as a coefficient in the equation if there is already a coefficient there, multiply it by the factor it must go in front of entire molecules, not between atoms within a molecule Recount and Repeat until Balanced

    17. 17 Examples when magnesium metal burns in air it produces a white, powdery compound magnesium oxide Mg(s) + O2(g) ® MgO(s)

    18. 18 Examples Under appropriate conditions at 1000°C ammonia gas reacts with oxygen gas to produce gaseous nitrogen monoxide and gaseous water NH3(g) + O2(g) ® NO(g) + H2O(g)

    19. 19 Aqueous Solutions Many times, the chemicals we are reacting together are dissolved in water mixtures of a chemical dissolved in water are called aqueous solutions Dissolving the chemicals in water helps them to react together faster the water separates the chemicals into individual molecules or ions the separate, free floating particles come in contact more frequently so the reaction speeds up

    20. 20 Predicting Whether a Reaction Will Occur in Aqueous Solution “forces” that drive a reaction formation of a solid formation of water formation of a gas transfer of electrons when chemicals (dissolved in water) are mixed and one of these 4 things can occur, the reaction will generally happen

    21. 21 Dissociation when ionic compounds dissolve in water, the anions and cations are separated from each other - this is called dissociation however not all ionic compounds are soluble in water! when compounds containing polyatomic ions dissociate, the polyatomic group stays together as one ion

    22. 22 Dissociation potassium iodide dissociates in water into potassium cations and iodide anions KI(aq) ? K+1(aq) + I-1(aq) copper(II) sulfate dissociates in water into copper(II) cations and sulfate anions CuSO4(aq) ? Cu+2(aq) + SO4-2(aq)

    23. 23 Dissociation potassium sulfate dissociates in water into potassium cations and sulfate anions K2SO4(aq) ? 2 K+1(aq) + SO4-2(aq)

    24. 24 Electrolytes electrolytes are substances whose water solution is a conductor of electricity all electrolyte have ions dissolved in water

    25. 25 Electrolytes in strong electrolytes, all the electrolyte molecules or formula units are separated into ions in weak electrolytes, a small percentage of the molecules are separated into ions in nonelectrolytes, none of the molecules are separated into ions

    26. 26 Types of Electrolytes salts = water soluble ionic compounds all strong electrolytes acids = form H+1 ions in water solution sour taste react and dissolve many metals strong acid = strong electrolyte, weak acid = weak electrolyte bases = water soluble metal hydroxides bitter taste, slippery (soapy) feeling solutions increases the OH-1 concentration

    27. 27 When will a Salt Dissolve? a compound is soluble in a liquid if it dissolves in that liquid NaCl is soluble in water, but AgCl is not a compound is insoluble if a significant amount does not dissolve in that liquid AgCl is insoluble in water though there is a very small amount dissolved, but not enough to be significant

    28. 28 When will a Salt Dissolve? Predicting whether a compound will dissolve in water is not easy The best way to do it is to do some experiments to test whether a compound will dissolve in water, then develop some rules based on those experimental results we call this method the empirical method

    29. 29 Solubility Rules Compounds that are Generally Soluble in Water

    30. 30 Solubility Rules Compounds that are Generally Insoluble

    31. 31 Using the Solubility Rules to Predict an Ionic Compound’s Solubility in Water first check the cation, if it is Li+, Na+, K+, or NH4+ then the compound will be soluble in water regardless of the anion! if the cation is not Li+, Na+, K+, or NH4+ then follow the rule for the anion if a rule says the compounds are mostly soluble, then the exceptions are insoluble but if a rule says the compounds are mostly insoluble, then the exceptions are soluble note: slightly soluble ? insoluble

    32. 32 Determine if Each of the Following is Soluble in Water KOH AgBr CaCl2 Pb(NO3)2 PbSO4

    33. 33 Determine if Each of the Following is Soluble in Water KOH Soluble, because the cation is K+ AgBr Insoluble, even though most compounds with Br- are soluble, this is an exception CaCl2 Soluble, most compounds with Cl- are soluble Pb(NO3)2 Soluble, because the anion is NO3- PbSO4 Insoluble, even though most compounds with SO42- are soluble, this is an exception

    34. 34 Precipitation Reactions many reactions are done by mixing aqueous solutions of electrolytes together when this is done, often a reaction will take place from the cations and anions in the two solutions exchanging if the ion exchange results in forming a compound that is insoluble in water, it will come out of solution as a precipitate

    35. 35 Precipitation Reactions

    36. 36 Precipitation Reactions

    37. 37 No Precipitate Formation = No Reaction

    38. 38 Process for Predicting the Products of a Precipitation Reaction Determine what ions each aqueous reactant has Exchange Ions (+) ion from one reactant with (-) ion from other Balance Charges of combined ions to get formula of each product Balance the Equation count atoms Determine Solubility of Each Product in Water use the Solubility Rules if product is insoluble or slightly soluble, it will precipitate if neither product will precipitate, no reaction

    39. 39 Example 7.7 - When an aqueous solution of sodium carbonate is added to an aqueous solution of copper(II) chloride, a white solid forms Write the formulas of the reactants Na2CO3(aq) + CuCl2(aq) ? Determine the ions present when each reactant dissociates (Na+ + CO32-) + (Cu+2 + Cl-) ? Exchange the Ions (Na+ + CO32-) + (Cu+2 + Cl-) ? (Na+ + Cl-) + (Cu+2 + CO32-)

    40. 40 Write the formulas of the products cross charges and reduce Na2CO3(aq) + CuCl2(aq) ? NaCl + CuCO3 Balance the Equation Na2CO3(aq) + CuCl2(aq) ? 2 NaCl + CuCO3 Example 7.7 - When an aqueous solution of sodium carbonate is added to an aqueous solution of copper(II) chloride, a white solid forms

    41. 41 Determine the solubility of each product NaCl is soluble CuCO3 is insoluble Write an (s) after the insoluble products and a (aq) after the soluble products Na2CO3(aq) + CuCl2(aq) ? 2 NaCl(aq) + CuCO3(s) Example 7.7 - When an aqueous solution of sodium carbonate is added to an aqueous solution of copper(II) chloride, a white solid forms

    42. 42 Ionic Equations equations which describe the chemicals put into the water and the product molecules are called molecular equations 2 KOH(aq) + Mg(NO3)2(aq) ® 2 KNO3(aq) + Mg(OH)2(s) equations which describe the actual dissolved species are called ionic equations aqueous electrolytes are written as ions soluble salts, strong acids, strong bases insoluble substances and nonelectrolytes written in molecule form solids, liquids and gases are not dissolved, therefore molecule form 2K+1(aq) + 2OH-1(aq) + Mg+2(aq) + 2NO3-1(aq) ® 2K+1(aq) + 2NO3-1(aq) + Mg(OH)2(s)

    43. 43 Ionic Equations ions that are both reactants and products are called spectator ions 2K+1(aq) + 2OH-1(aq) + Mg+2(aq) + 2NO3-1(aq) ® 2K+1(aq) + 2NO3-1(aq) + Mg(OH)2(s)

    44. 44 Acid-Base Reactions also called neutralization reactions because the acid and base neutralize each others properties in the reaction of an acid with a base, the H+1 from the acid combines with the OH-1 from the base to make water the cation from the base combines with the anion from the acid to make the salt acid + base ???salt + water 2 HNO3(aq) + Ca(OH)2(aq) ? Ca(NO3)2(aq) + 2 H2O(l) the net ionic equation for an Acid-Base reaction is H+1(aq) + OH-1(aq) ? H2O(l) as long as the salt that forms is soluble in water

    45. 45 Example 7.11 - Write the molecular, ionic and net-ionic equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide Write the formulas of the reactants HNO3(aq) + Ca(OH)2(aq) ? Determine the ions present when each reactant dissociates (H+ + NO3-) + (Ca+2 + OH-) ? Exchange the ions, H+1 combines with OH-1 to make H2O(l) (H+ + NO3-) + (Ca+2 + OH-) ? (Ca+2 + NO3-) + H2O(l)

    46. 46 Write the formulas of the products cross charges and reduce HNO3(aq) + Ca(OH)2(aq) ? Ca(NO3)2 + H2O(l) Balance the Equation may be quickly balanced by matching the numbers of H and OH to make H2O coefficient of the salt is always 1 2 HNO3(aq) + Ca(OH)2(aq) ? Ca(NO3)2 + 2 H2O(l) Example 7.11 - Write the molecular, ionic and net-ionic equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide

    47. 47 Determine the solubility of the salt Ca(NO3)2 is soluble Write an (s) after the insoluble products and a (aq) after the soluble products 2 HNO3(aq) + Ca(OH)2(aq) ? Ca(NO3)2(aq) + 2 H2O(l) Example 7.11 - Write the molecular, ionic and net-ionic equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide

    48. 48 Example 7.11 - Write the molecular, ionic and net-ionic equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide Dissociate all aqueous materials to get complete ionic equation not H2O 2 H+(aq) + 2 NO3-(aq) + Ca+2(aq) + 2 OH-(aq) ? Ca+2(aq) + 2 NO3-(aq) + H2O(l) Eliminate spectator ions to get net-ionic equation 2 H+1(aq) + 2 OH-1(aq) ? 2 H2O(l) H+1(aq) + OH-1(aq) ? H2O(l)

    49. 49 Gas Evolving Reactions Some reactions form a gas directly from the ion exchange K2S(aq) + H2SO4(aq) ? K2SO4(aq) + H2S(g) Other reactions form a gas by the decomposition of one of the ion exchange products into a gas and water K2SO3(aq) + H2SO4(aq) ? K2SO4(aq) + H2SO3(aq) H2SO3 ? H2O(l) + SO2(g)

    50. 50 Compounds that Undergo Gas Evolving Reactions

    51. 51 Process for Predicting the Products of a Gas Evolving Reaction Determine what ions each aqueous reactant has Exchange Ions (+) ion from one reactant with (-) ion from other Balance Charges of combined ions to get formula of each product Check to see if either product is H2S Check to see if either product decomposes, if so rewrite as H2O(l) and a gas see table Balance the Equation Determine Solubility of Other Product in Water

    52. 52 Example - When an aqueous solution of sodium sulfite is added to an aqueous solution of nitric acid, a gas evolves Write the formulas of the reactants Na2SO3(aq) + HNO3(aq) ? Determine the ions present when each reactant dissociates (Na+1 + SO3-2) + (H+1 + NO3-1) ? Exchange the Ions (Na+1 + SO3-2) + (H+1 + NO3-1) ? (Na+1 + NO3-1) + (H+1 + SO3-2)

    53. 53 Write the formulas of the products cross charges and reduce Na2SO3(aq) + HNO3(aq) ? NaNO3 + H2SO3 Check to see either product H2S - No Check to see of either product decomposes – Yes H2SO3 decomposes into SO2(g) + H2O(l) Na2SO3(aq) + HNO3(aq) ? NaNO3 + SO2(g) + H2O(l) Example - When an aqueous solution of sodium sulfite is added to an aqueous solution of nitric acid, a gas evolves

    54. 54 Balance the Equation Na2SO3(aq) + 2 HNO3(aq) ? 2 NaNO3 + SO2(g) + H2O(l) Determine the solubility of other product NaNO3 is soluble Write an (s) after the insoluble products and a (aq) after the soluble products Na2SO3(aq) + 2 HNO3(aq) ? 2 NaNO3(aq) + SO2(g) + H2O(l) Example - When an aqueous solution of sodium sulfite is added to an aqueous solution of nitric acid, a gas evolves

    55. 55 Other Patterns in Reactions the precipitation, acid-base, and gas evolving reactions all involved exchanging the ions in the solution other kinds of reactions involve transferring electrons from one atom to another – these are called oxidation-reduction reactions also known as redox reactions unlike the others, many of these reactions are not done by dissolving the reactants in water

    56. 56 Oxidation-Reduction Reactions We say that the element that loses electrons in the reaction is oxidized and the substance that gains electrons in the reaction is reduced you cannot have one without the other

    57. 57 Reactions of Metals with Nonmetals (Oxidation-Reduction) metals react with nonmetals to form ionic compounds ionic compounds are solids at room temperature the metal loses electrons and becomes a cation the metal undergoes oxidation the nonmetal gains electrons and becomes an anion the nonmetal undergoes reduction In the reaction, electrons are transferred from the metal to the nonmetal 2 Na(s) + Cl2(g) ? NaCl(s)

    58. 58 Oxidation-Reduction Reactions any reaction that has an element that is uncombined on one side and combined on the other is a redox reaction uncombined = free element 2 CO + O2 ? 2 CO2 2 N2O5 ? 4 NO2 + O2 3 C + Fe2O3 ? 3 CO + 2 Fe Mg + Cl2 ? MgCl2 any reaction where a cation changes charge is redox CuCl + FeCl3 ? FeCl2 + CuCl2 SnCl2 + F2 ? SnCl2F2

    59. 59 Combustion Reactions Reactions in which O2(g) is a reactant are called Combustion Reactions Combustion reactions release lots of energy Combustion reactions are a subclass of Oxidation-Reduction reactions

    60. 60 Combustion Products to predict the products of a combustion reaction, combine each element in the other reactant with oxygen

    61. 61 Classifying Reactions one way is based on the process that happens precipitation, neutralization, formation of a gas, or transfer of electrons

    62. 62 Classifying Reactions another scheme classifies reactions by what the atoms do

    63. 63 Synthesis Reactions also known as Composition or Combination reactions two (or more) reactants combine together to make one product simpler substances combining together 2 CO + O2 ® 2 CO2 2 Mg + O2 ® 2 MgO HgI2 + 2 KI ® K2HgI4

    64. 64 Decomposition Reactions a large molecule is broken apart into smaller molecules or its elements caused by addition of energy into the molecule have only one reactant, make 2 or more products

    65. 65 Decomposition of Water

    66. 66 Displacement Reactions also known as single-displacement reactions Reactions that involve one anion being transferred from one cation to another X ÅYq + A ® X + AÅYq Zn(s) + 2 HCl(aq) ? ZnCl2(aq) + H2(g) Fe2O3(s) + Al(s) ? Fe(s) + Al2O3(s) 2 Na(s) + 2 H2O(aq) ? 2 NaOH(aq) + H2(g)

    67. 67 Displacement of Copper by Zinc

    68. 68 Double Displacement Reactions two ionic compounds exchange ions may be followed by decomposition of one of the products to make a gas X ÅYq (aq) + A ÅBq (aq) ® XB + AY precipitation, acid-base and gas-evolving reactions are also double displacement reactions

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