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Unit 7: Chemical Equations

Honors 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. Honors 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 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.

  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. use one N/A

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

  7. coefficients To balance, modify only __________. subscript Changing a ________ changes the substance. superscripts Right now, ___________ don’t enter into our “balancing” picture. The thermite reaction (2 Al + Fe2O3 2 Fe + Al2O3) releases enough heat that it is used for underwater welding.

  8. 4 2 SiCl4 + H2O  SiO2 + HCl SiClClClCl HHO SiOO HCl HCl HHO HCl HCl Rule of Thumb A:Save the simplest substances for last (i.e., choose a complex substance on each side first). 3 2 3 Au2S3 + H2 Au + H2S AuAuSSS HH Au HHS HHS HHS HH Au HH

  9. 6 2 3 V2O5 + HCl  VOCl3 + H2O VVOOOOO HCl HCl VOClClCl HHO HCl HHO HCl VOClClCl HHO HCl HCl

  10. Rule of Thumb B: If polyatomic ions are the same on both sides of the equation, balance them first. 3 2 6 Hg(OH)2 + H3PO4 Hg3(PO4)2 + H2O HgOHOH HHH# HgHgHg## HHO HHO HgOHOH HHO HHO HHH# HgOHOH HHO HHO

  11. CaC2(s) + H2O(l) C2H2(g) + CaO(s) CaSi2 + SbI3 Si + Sb + CaI2 Al + CH3OH Al(CH3O)3 + H2 3 2 6 2 3 3 2 6 2 3 2 2 5 4 2 C2H2(g) + O2(g) CO2(g) + H2O(l) ** C3H8 + O2 CO2 + H2O 5 3 4 ** 8 5 6 C5H12 + O2 CO2 + H2O ** complete combustion of a hydrocarbon yields CO2 and H2O ** =

  12. 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… -- synonyms: “soluble” or “in solution” -- acids and bases are aqueous solutions

  13. 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

  14. 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.

  15. clear Na2CO3 solution clear Ca(NO3)2 solution (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)

  16. 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

  17. 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)

  18. Methane gas (CH4) burns in oxygen. Much of the methane that is liberated during the extraction of petroleum is simply burned because the cost of transporting it is too high. 2 2 CH4(g) O2(g) H2O(g) CO2(g) + + Write an equation for the combustion of C8H18. 25 8 9 2 16 18 C8H18 + O2 CO2 + H2O

  19. four types A + B AB AB + C ABC A + B + C ABC Classifying Reactions synthesis: simpler substances combine to form more complex substances sodium + chlorine gas sodium chloride + Na 2 NaCl 2 Cl2

  20. AB A + B ABC AB + C ABC A + B + C lithium chlorate lithium chloride + oxygen decomposition: complex substances are broken down into simpler ones Li+ Li+ ClO3– Cl– 2 2 3 + O2 LiClO3 LiCl

  21. AB + C A + CB AB + C B + AC copper(II) sulfate aluminum sulfate aluminum copper + + single-replacement: one element replaces another ? Cu2+ SO42– Al3+ SO42– + + 2 3 3 Al CuSO4 Cu Al2(SO4)3

  22. AB + CD lead(IV) nitrate lead(IV) oxide calcium oxide calcium nitrate + + double-replacement: AD + CB ? Pb4+ NO3– O2– Ca2+ 2 2 Pb(NO3)4 CaO PbO2 Ca(NO3)2 + +

  23. 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. Fe + BaSO4 3 2 2 3 Cr + Mg(ClO3)2 NR NaCl + Br2 2 2 NR CoF2 + Br2

  24. 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. 2 2 PbI2(s) + KNO3(aq) (?) (?) Pb2+ Pb2+ I– I– NO3– K+ K+ NO3– (ppt) (aq) K2SO4(aq) + H2O(l) 2 2 (?) (?) K+ OH– H+ K+ H+ OH– SO42– SO42– (aq) (water) NR Fe3+ Cu2+ Cl– NO3– (aq) (aq)

  25. 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. **

  26. SUBSTANCE “B” SUBSTANCE “A” Use coeff. from bal. eq. to go from “moles of A” to “moles of B” Mass Mass Vol. Vol. MOL MOL (unknown) (known) Part. Part.

  27. 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 = 4.20 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 = 1.47 mol Na 2 mol Na2O

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