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Unit 7: Chemical Equations

Chemistry. Unit 7: Chemical Equations. In a reaction: . atoms are rearranged . mass . AND . are conserved . energy . charge . Balancing Chemical Equations. law of conservation of mass. same # of atoms of each type on each side of equation. =. CH 4 + 2 O 2  CO 2 + 2 H 2 O.

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Unit 7: Chemical Equations

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  1. Chemistry Unit 7: Chemical Equations

  2. In a reaction: atoms are rearranged mass AND are conserved energy charge Balancing Chemical Equations law of conservation of mass same # of atoms of each type on each side of equation =

  3. 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

  4. + 1 1 1 ___Fe2(s) ___O3(g) ___Fe2O3(s) EX. solid iron reacts with oxygen gas to yield solid iron (III) oxide Fe3+ O2– + ___Fe(s) ___O2(g) ___Fe2O3(s) If all coefficients are 1… + 1 1 1 ___Fe(s) ___O2(g) ___Fe2O3(s) + But we can’t!!! If we change subscripts… +

  5. + ___Fe(s) ___O2(g) ___Fe2O3(s) subscript Changing a ___________ changes the substance. coefficients To balance, modify only _____________. superscripts Right now, _______________ don’t enter into our “balancing” picture. 4 3 2 + Hint: Start with most complicated substances first and leave simplest substances for last.

  6. solid sodium reacts w/oxygen to form solid sodium oxide Na+ O2– 4 1 2 ___Na(s) + ___O2(g) ___Na2O(s) + Aqueous aluminum sulfate reacts w/aqueous calcium chloride to form a white precipitate of calcium sulfate. The other compound remains in solution. Ca2+ Al3+ SO42– Cl– 1 3 3 2 + + _ AlCl3 _ CaSO4 _ Al2(SO4)3 _ CaCl2 (aq) (s) (aq) (aq)

  7. Furnaces burn primarily methane. _ CaC2(s) + _ H2O(l) _ C2H2(g) + _ CaO(s) _ CaSi2 + _ SbI3 _ Si + _ Sb + _ CaI2 _ Al + _ CH3OH _ Al(CH3O)3 + _ H2 Methane gas (CH4) reacts with oxygen to form carbon dioxide gas and water vapor. 1 2 1 2 _ CH4(g) _ O2(g) _ H2O(g) _ CO2(g) + + 1 1 1 1 3 2 6 2 3 3 1 2 6 2 3

  8. 1 2 1 2 5 4 2 _ C2H2(g) + _ O2(g) _ CO2(g) + _ H2O(l) ** Odd # Oxy 1 5 3 4 _ C3H8 + _ O2 _ CO2 + _ H2O ** 1 8 5 6 _ C5H12 + _ O2 _ CO2 + _ H2O ** complete combustion (+ O2) of a hydrocarbon (CxHy) yields CO2 and H2O ** = Write equations for the combustion of C7H16 and C8H18 1 11 7 8 _ C7H16 + _ O2 _ CO2 + _ H2O 1 25 8 9 2 16 18 _ C8H18 + _ O2 _ CO2 + _ H2O Odd # Oxy

  9. 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

  10. For a reaction to occur, particles of reactants must collide, and with sufficient energy Evidence of a chemical reaction: odor light heat gas emitted sound color change A reaction has occurred if the chemical and physical properties of the reactants and products differ. collision theory

  11. exothermic reactions endothermic reactions energy needed to start a reaction activation energy: Chemical reactions release or absorb energy. The reaction in an oxy- acetylene torch is exothermic. Photosynthesis is an endothermic reaction.

  12. Activation Energy Endothermic Reaction Energy + Reactants  Products Products Energy Reactants Reaction progress

  13. Exothermic Reaction Reactants  Products + Energy 10 energy = 8 energy + 2 energy Energy of reactants Energy of products Reactants Energy Products Reaction Progress

  14. Decomposition of Nitrogen Triiodide N2 NI3 I2 2 NI3(s) N2(g) + 3 I2(g)

  15. AE AE catalyst: speeds up reaction w/o being consumed it lowers the activation energy (Ea) … without catalyst with catalyst Energy time time Examples: enzymes catalyze biochemical reactions catalytic converters convert CO into CO2

  16. Reaction Conditions and Terminology Certain symbols give more info about a reaction (s) = solid (l) = liquid (g) = gas (aq) = aqueous (dissolved in H2O) NaCl(s) NaCl(aq) More on aqueous… “soluble” or “in solution” indicates that a substance is dissolved in water (usually) all acids are aqueous solutions

  17. means... means ______ is added to the reaction MgCO3(s) MgO(s) + CO2(g) C6H5Cl + NaOH C6H5OH + NaCl C2H4(g) + H2(g) C2H6(g) Other symbols… (i.e., clues about the reaction) “yields” or “produces” heat Temp. at which we perform rxn. might be given. 400oC The catalyst used might be given. Pt

  18. 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 All compounds… CxHy + O2 CO2 + H2O Combustion reaction (of a hydrocarbon) Ause activity series to predict products/reactivity Buse solubility chart to predict products/reactivity

  19. Balance and classify the following reactions: 1 1 1 1 _ F2 _ I2 _ MgI2 _ MgF2 + + Single replacement 10 1 + _ O2 + _ H2O 12 6 + _ CO2 4 _ N2 _ C3H5N3O9 Decomposition 1 8 5 6 _ C5H12 + _ O2 _ CO2 + _ H2O Double Replacement? Combustion

  20. Word Equations Solid iron reacts with oxygen gas to yield solid iron(III) oxide. word equation: iron + oxygen  iron(III) oxide Fe3+ O2– balanced equation: 4 Fe + 3 O2  2 Fe2O3

  21. Write a balanced equation (w/rxn conditions) from the following word equations. Solid sodium reacts w/oxygen to form solid sodium oxide. Na+ O2– 4 2 Na(s) + O2(g) Na2O(s) + Aqueous aluminum sulfate reacts w/aqueous calcium chloride to form a white precipitate of calcium sulfate. The other compound remains in solution. Ca2+ Al3+ SO42– Cl– 3 3 2 + + AlCl3 CaSO4 Al2(SO4)3 CaCl2 (aq) (s) (aq) (aq)

  22. 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

  23. AB + C A + CB AB + C B + AC sodium bromide sodium chloride chlorine bromine + + copper (II) sulfate aluminum sulfate aluminum copper + + single-replacement: one element replaces another Na+ Na+ Br– Cl– 1 2 2 1 _ Cl2 _ Br2 _ NaBr _ NaCl + + ? Cu2+ SO42– Al3+ SO42– + + 2 3 1 3 _ Al _ CuSO4 _ Cu _ Al2(SO4)3

  24. Ca Printable Version of Activity Series Activity Series Element Reactivity Li Rb K Ba Ca Na Mg Al Mn Zn Cr Fe Ni Sn Pb H2 Cu Hg Ag Pt Au Foiled again: Aluminum is knocked out by Calcium Halogen Reactivity F2 Cl2 Br2 I2

  25. Predict if these reactions will occur Al + MgCl2 3 2 2 3 Mg + AlCl3 Can magnesium replace aluminum? • Activity Series YES, magnesium is more reactive than aluminum. NR (No Reaction) Al + MgCl2 Can aluminum replace magnesium? Therefore, no reaction will occur. NO, magnesium is less reactive than aluminum. Order of reactants DOES NOT determine how they react. No reaction MgCl2 + Al We must determine if the lone element is more reactive than the bonded one… metals replace metals or non-metals replace nonmetals

  26. _ Ba + _ FeSO4 _ Mg + _ Cr(ClO3)3 _ Pb + _ Al2O3 _ NaBr + _ Cl2 _ FeCl3 + _ I2 _ CoBr2 + _ F2 How do we know if a reaction will occur? For single-replacement reactions, use Activity Series. In general, elements above replace elements below. 1 1 1 1 _ Fe + _ BaSO4 3 2 2 3 _ Cr + _ Mg(ClO3)2 NR _ NaCl + _ Br2 2 1 2 1 NR 1 1 1 1 _ CoF2 + _ Br2

  27. iron (III) chloride iron (III) hydroxide potassium hydroxide potassium chloride + + AB + CD lead (IV) nitrate lead (IV) oxide calcium oxide calcium nitrate + + double-replacement: AD + CB ? Fe3+ Fe3+ Cl– Cl– K+ OH– OH– K+ 1 3 1 3 _ FeCl3 _ KOH _ Fe(OH)3 _ KCl + + ? Pb4+ Pb4+ O2– O2– NO3– Ca2+ Ca2+ NO3– 1 2 1 2 _ Pb(NO3)4 _ CaO _ PbO2 _ Ca(NO3)2 + +

  28. Double Replacement Reactions Formation of a solid: AgCl AgNO3(aq) + KCl(aq)  KNO3 (aq) + AgCl(s)

  29. precipitate: a solid product that forms in an aqueous solution reaction When ionic substances have “(aq)” written after them, the individual ions have dissociated from the ionic crystal and are floating around separately. Na3PO4(aq) means… 3 Na+(aq) + PO43–(aq) Sodium phosphate, Na3PO4, (sometimes called “sodium phosphate, tribasic”) is a cleaning agent and food preservative.

  30. clear Na2CO3 solution clear Ca(NO3)2 solution precipitate: a solid product that forms in an aqueous solution reaction (aq) (aq) Na2CO3 + Ca(NO3)2 (aq) (s) 2 NaNO3 CaCO3 + “chunks” NO3– Na+ “sinkies” Ca2+ CO32– NO3– Na+ “floaties” ppt cloudy solution containing CaCO3(s) and NaNO3(aq)

  31. Na2CO3 FeCO3 FeCl2 NaCl + + (aq) (s) Predict if a reaction will occur when you combine aqueous solutions of iron (II) chloride and sodium carbonate… If the reaction does occur, write a balanced chemical equation showing it (be sure to include phase notation). Balanced chemical equation iron (II) carbonate iron (II) chloride + sodium carbonate + sodium chloride CO32- CO32- Na+ Fe2+ Fe2+ Cl - Cl- Na+ CO3 FeCO3 Na2 Cl2 Fe NaCl (aq) (s) Using the SOLUBILITY TABLE: sodium chloride is soluble iron (II) carbonate is insoluble 2 (aq) (aq)

  32. _ Pb(NO3)2(aq) + _ KI(aq) _ KOH(aq) + _ H2SO4(aq) _ FeCl3(aq) + _ Cu(NO3)2(aq) (?) (?) Fe3+ Cu2+ Cl– NO3– For double-replacement reactions, reaction will occur if any product is: water a gas a precipitate driving forces Check new combinations to decide. 1 2 1 2 _ PbI2(s) + _ KNO3(aq) (?) (?) Pb2+ Pb2+ I– I– NO3– K+ K+ NO3– (ppt) (aq) _ K2SO4(aq) + _ H2O(l) 2 1 1 2 (?) (?) OH– K+ OH– H+ SO42– K+ SO42– H+ (aq) (water) NR Fe3+ Cu2+ Cl– NO3– (aq) (aq)

  33. NO3– NO3– Pb2+ Pb2+ NO3– NO3– I– Na+ Na+ I– Ions in Aqueous Solution Pb(NO3)2(aq) Pb(NO3)2(s) Pb2+(aq) + 2 NO3–(aq) add water dissociation: “splitting into ions” NaI(aq) NaI(s) Na+(aq) + I–(aq) add water ChemThink

  34. yields 1 2 1 __Pb2+(aq) + __I–(aq) __PbI2(s) I– I– I– I– I– I– I– I– NO3– NO3– Na+ Na+ Na+ Na+ Pb2+ Pb2+ Pb2+ Pb2+ NO3– NO3– Mix them and get the overall ionic equation… reactants 1 2 2 2 __Pb2+(aq) + __NO3–(aq) + __Na+(aq) + __I–(aq) 1 2 2 + __NO3–(aq) + __Na+(aq) __PbI2(s) products Cancel spectator ions to get net ionic equation…

  35. Polymers and Monomers polymer: a large molecule (often a chain) made of many smaller molecules called monomers Polymers can be made more rigid if the chains are linked together by way of a cross-linking agent.

  36. H H O H–N–C–C–O–H R Monomer Polymer aminoacids………… proteins nucleotides (w/N- bases A,G,C,T/U)….. nucleic acids styrene……………… polystyrene PVA…………………. “slime” polyvinyl alcohol

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