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Unit 7: Chemical Equations

Chemistry. Unit 7: Chemical Equations. 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

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Unit 7: Chemical Equations

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  1. Chemistry Unit 7: Chemical Equations

  2. 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

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

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

  5. 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” also indicate that a substance is dissolved in water (usually) -- acids are aqueous solutions

  6. 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

  7. 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” NO31– Na1+ “sinkies” Ca2+ CO32– NO31– Na1+ “floaties” ppt cloudy solution containing CaCO3(s) and NaNO3(aq)

  8. 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 =

  9. + 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) + If we change subscripts… +

  10. + ___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.

  11. solid sodium reacts w/oxygen to form solid sodium oxide Na1+ 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– Cl1– 1 3 3 2 + + _ AlCl3 _ CaSO4 _ Al2(SO4)3 _ CaCl2 (aq) (s) (aq) (aq)

  12. 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

  13. 1 2 1 2 5 4 2 _ C2H2(g) + _ O2(g) _ CO2(g) + _ H2O(l) ** 1 5 3 4 _ C3H8 + _ O2 _ CO2 + _ H2O ** 1 8 5 6 _ C5H12 + _ O2 _ CO2 + _ H2O ** complete combustion of a hydrocarbon 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

  14. four types A + B AB AB + C ABC A + B + C ABC Classifying Reactions synthesis: simpler substances combine to form more complex substances oxygen + rhombic sulfur sulfur dioxide 8 1 8 + __ O2 __ SO2 __ S8 sodium + chlorine gas sodium chloride + __ Na 2 1 __ NaCl 2 __ Cl2

  15. AB A + B ABC AB + C ABC A + B + C lithium chlorate lithium chloride + oxygen water hydrogen gas + oxygen gas decomposition: complex substances are broken down into simpler ones Li1+ Li1+ ClO31– Cl1– 2 2 1 1 3 + _ O2 _ LiClO3 _ LiCl 2 2 1 + _ O2 _ H2O _ H2

  16. 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 Na1+ Na1+ Br1– Cl1– 1 2 2 1 _ Cl2 _ Br2 _ NaBr _ NaCl + + ? Cu2+ SO42– Al3+ SO42– + + 2 3 1 3 _ Al _ CuSO4 _ Cu _ Al2(SO4)3

  17. 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+ Cl1– Cl1– K1+ OH1– OH1– K1+ 1 3 1 3 _ FeCl3 _ KOH _ Fe(OH)3 _ KCl + + ? Pb4+ Pb4+ O2– O2– NO31– Ca2+ Ca2+ NO31– 1 2 1 2 _ Pb(NO3)4 _ CaO _ PbO2 _ Ca(NO3)2 + +

  18. _ 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

  19. _ Pb(NO3)2(aq) + _ KI(aq) _ KOH(aq) + _ H2SO4(aq) _ FeCl3(aq) + _ Cu(NO3)2(aq) (?) (?) Fe3+ Cu2+ Cl1– NO31– 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+ I1– I1– NO31– K1+ K1+ NO31– (ppt) (aq) _ K2SO4(aq) + _ H2O(l) 2 1 1 2 (?) (?) K1+ OH1– H1+ SO42– K1+ SO42– H1+ OH1– (aq) (water) NR Fe3+ Cu2+ Cl1– NO31– (aq) (aq)

  20. NO31– NO31– Pb2+ Pb2+ NO31– NO31– I1– Na1+ Na1+ I1– Ions in Aqueous Solution Pb(NO3)2(aq) Pb(NO3)2(s) Pb2+(aq) + 2 NO31–(aq) add water dissociation: “splitting into ions” NaI(aq) NaI(s) Na1+(aq) + I1–(aq) add water

  21. yields 1 2 1 __Pb2+(aq) + __I1–(aq) __PbI2(s) I1– I1– I1– I1– I1– I1– I1– I1– NO31– NO31– Na1+ Na1+ Na1+ Na1+ Pb2+ Pb2+ Pb2+ Pb2+ NO31– NO31– Mix them and get the overall ionic equation… reactants 1 2 2 2 __Pb2+(aq) + __NO31–(aq) + __Na1+(aq) + __I1–(aq) 1 2 2 + __NO31–(aq) + __Na1+(aq) __PbI2(s) products Cancel spectator ions to get net ionic equation…

  22. OH1– NO31– clear Zn(NO3)2 solution clear Ba(OH)2 solution Ba2+ Zn2+ OH1– NO31– Mix together Zn(NO3)2(aq) and Ba(OH)2(aq): Zn(NO3)2(aq) Ba(OH)2(aq) Zn2+(aq) + 2 NO31–(aq) Ba2+(aq) + 2 OH1–(aq)

  23. OH1– OH1– OH1– OH1– NO31– yields OH1– OH1– OH1– OH1– NO31– Zn2+ Zn2+ Ba2+ Ba2+ Zn2+ Zn2+ NO31– NO31– Mix them and get the overall ionic equation… reactants 1 2 1 2 __Zn2+(aq) + __NO31–(aq) + __Ba2+(aq) + __OH1–(aq) 1 2 1 + __NO31–(aq) + __Ba2+(aq) __Zn(OH)2(s) products Cancel spectator ions to get net ionic equation… 1 2 1 __Zn2+(aq) + __OH1–(aq) __Zn(OH)2(s)

  24. 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.

  25. 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

  26. 4 Na(s) + O2(g) 2 Na2O(s) Quantitative Relationships in Chemical Equations Coefficients of a balanced equation represent # of particles OR # of moles, but NOT # of grams. **

  27. mass mass vol. vol. MOL MOL part. part. 4 Na(s) + 1 O2(g) 2Na2O(s) When going from moles of one substance to moles of another, use coefficients from balanced equation. Use coeff. from balanced equation in crossing this bridge SUBSTANCE “B” SUBSTANCE “A” (unknown) (known)

  28. 4 Na(s) + O2(g) 2 Na2O(s) ( ) ( ( ) ) Na2O Na Na2O Na O2 How many moles oxygen will react with 16.8 moles sodium? 1 mol O2 16.8 mol Na = 4.2 mol O2 4 mol Na How many moles sodium oxide are produced from 87.2 moles sodium? 2 mol Na2O 87.2 mol Na = 43.6 mol Na2O 4 mol Na How many moles sodium are required to produce 0.736 moles sodium oxide? 4 mol Na 0.736 mol Na2O = 1.472 mol Na 2 mol Na2O

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