1. Unit 9:Chemical Reactions

2. Bellringer 10/15 List 4 signs that let you know achemical reaction has occurred. 3. Objectives Follow directions Identify a cause and effectrelationship in balancingchemical reactions Balance Chemical reactions List the signs of a chemicalreaction 4. Introduction Chemical reactions occur when bondsbetween the outermost parts of atoms areformed or broken Chemical reactions involve changes inmatter, the making of new materials withnew properties, and energy changes. Symbols represent elements, formulasdescribe compounds, chemical equationsdescribe a chemical reaction 5. Parts of a ReactionEquation Chemical equations show the conversion ofreactants (the molecules shown on the left ofthe arrow) into products (the molecules shownon the right of the arrow). A + sign separates molecules on the same side The arrow is read as yields ExampleC + O2 CO2 This reads carbon plus oxygen react to yield carbon dioxide 6. Chemical EquationsTheir Job: Depict the kind ofreactants and products and theirrelative amounts in a reaction.4 Al (s) + 3 O2 (g) ---> 2 Al2O3 (s)The numbers in the front are calledCoefficientsThe letters (s), (g), and (l) are thephysical states of compounds. 7. Chemical EquationsContinued You can indicate the physical stateof a substance by putting a symbolafter each formula. (s) solid (l) liquid (g) gas (aq) aqueous solution (in water)For example: K(s) + Cl(g) KCl(s) 8. Conservation of Matter Matter cannot be created ordestroyed. It can change forms Total mass in reactants mustequal total mass of products 9. Terms with Equations Activation energyminimumenergy colliding particles musthave in order to react Endothermic reactionprocessthat absorbs heat from thesurroundings Exothermic reactionprocessthat releases heat to thesurroundings 10. Preview/Predict Looking at the two rxns, labelone as endothermic & one asexothermic. Explain why. SP 11. Catalysts A substanceused to speed upthe rate of areaction. Neither aproduct nor areactant. Written abovethe arrow. 12. Symbols Used inEquations Solid ___ Liquid ___ Gas ___ Aqueous solution ___H2SO4 Catalyst Escaping gas () Change of temperature () 13. The charcoal used in a grill is basically carbon. Thecarbon reacts with oxygen to yield carbon dioxide. Thechemical equation for this reaction, C + O2 CO2, contains the same information as the Englishsentence but has quantitative meaning as well. 14. Chemical EquationsBecause 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. Balancing Equations When balancing a chemical reaction youmay add coefficients in front of thecompounds to balance the reaction, but you may not change the subscripts. Changing the subscripts changes thecompound. Subscripts are determinedby the valence electrons (charges forionic or sharing for covalent) 16. Subscripts vs. Coefficients The subscripts tell you how many atoms of a particular element are in a compound. The coefficient tells you about the quantity, or number, of molecules of the compound. 17. Chemical Equations4 Al(s) + 3 O2(g)---> 2 Al2O3(s)This equation means4 Al atoms + 3 O2 molecules---produces--->2 molecules of Al2O3 AND/OR4 moles of Al + 3 moles of O2 ---produces---> 2 moles of Al2O3 18. Steps to BalancingEquationsThere are four basic steps to balancing a chemical equation. 1. Write the correct formula for the reactants and theproducts. DO NOT TRY TO BALANCE IT YET! You mustwrite the correct formulas first. And most importantly, onceyou write them correctly DO NOT CHANGE THEFORMULAS! 2. Find the number of atoms for each element on the left side.Compare those against the number of the atoms of thesame element on the right side. 3. Determine where to place coefficients in front of formulasso that the left side has the same number of atoms as theright side for EACH element in order to balance theequation. 4. Check your answer to see if: The numbers of atoms on both sides of the equation are now balanced. The coefficients are in the lowest possible whole number ratios. (reduced) 19. Some Suggestions to Help YouSome Helpful Hints for balancing equations: Take one element at a time, working left to rightexcept for H and O. Save H for next to last, and Ountil last. IF everything balances except for O, and there is noway to balance O with a whole number, double allthe coefficients and try again. (Because O isdiatomic as an element) (Shortcut) Polyatomic ions that appear on bothsides of the equation should be balanced asindependent units 20. Balancing Equations 2 2___ H2(g) + ___ O2(g) ---> ___ H2O(l) What Happened to the Other Oxygen Atom????? This equation is not balanced! Two hydrogen atoms from a hydrogen molecule (H2) combines with one of the oxygen atoms from an oxygen molecule (O2) to form H2O. Then, the remaining oxygen atom combines with two more hydrogen atoms (from another H2 molecule) to make a second H2O molecule. 21. Balancing Equations 23 ___ Al(s) + ___ Br2(l) ---> ___ Al2Br6(s) 22. Balancing Equations____C3H8(g) + _____ O2(g) ---->_____CO2(g) + _____ H2O(g) 23. ____B4H10(g) + _____ O2(g) ----> ___ B2O3(g) + _____ H2O(g) 24. Balancing EquationsSodium phosphate + iron (III) oxide sodium oxide + iron (III) phosphate Na3PO4 +Fe2O3 ---->Na2O +FePO4 25. Diatomic Elements Fluorine F2 Chlorine Cl2 Bromine Br2 Iodine I2 Hydrogen H2 Nitrogen N2 Oxygen O2 26. Bellringer List and describe the five typesof chemical reactions listed inyour book. 27. Types of Reactions There are five types of chemicalreactions we will talk about:1. Synthesis reactions2. Decomposition reactions3. Single displacement reactions4. Double displacement reactions5. Combustion reactions You need to be able to identifythe type of reaction and predictthe product(s) 28. Steps to Writing Reactions Some steps for doing reactions 1. Identify the type of reaction 2. Predict the product(s) using the typeof reaction as a model 3. Balance it Dont forget about the diatomicelements! (BrINClHOF) Forexample, Oxygen is O2 as an element. In a compound, it cant be a diatomicelement because its not an elementanymore, its a compound! 29. 1. Combination or Synthesis Two or more substances combine to form a single substance. Forms only ONE PRODUCT! R + S RSFor Example: Al + N2 AlN 30. Practice Predict the products. Write and balancethe following synthesis reactionequations. Sodium metal reacts with chlorine gasNa(s) + Cl2(g) Solid Magnesium reacts with fluorinegasMg(s) + F2(g) Aluminum metal reacts with fluorine gasAl(s) + F2(g) 31. 2. Decomposition A single compound is brokendown into two or moreproducts. Has only ONE REACTANT! RS R + S 32. Practice Predict the products. Then,write and balance the followingdecomposition reactionequations: Solid Lead (IV) oxidedecomposesPbO2(s) Aluminum nitride decomposesAlN(s) 33. PracticeIdentify the type of reaction foreach of the following synthesisor decomposition reactions,and write the balancedequation: Nitrogen monoxideN2(g) + O2(g) BaCO3(s) (make Co be +3)Co(s)+ S(s) NI3(s) 34. Bellringer 10/19 Predict the products of thefollowing single replacementreaction, then balance thereaction, and correctly nameeach product:NaCl(s) + F2(g) When you are done pick up your lab book. 35. Free Response IN Your Lab Book: Write an outline for the followingprompt:When exposed to the natural elementsIron metal reacts with oxygen gas. Inthis natural state Iron usually has anoxidation state of +3. Tell what typereaction this is, write a balancedchemical equation, give the oxidationstate for oxygen, and identify whatsubstance is reduced in this reaction,and tell why that substance isreduced. 36. Bellringer Pick up a worksheet from thefront desk. Tear a sheet of paper in half,widthwise, and label it JanuaryPreTest Read the passages and answerthe questions in the order theyoccur (#s are messed up) 37. 3. Single-ReplacementReactions An element replaces anotherelement in a compound. Whether one metal will displaceanother metal is determined by theactivity series of metals chart. A reactive metal will replace anymetal listed below it in the activityseries. For example, Mg will replaceZn. T + RS TS + R When water splits it splits into H & OH 38. Single ReplacementReactions Write and balance the followingsingle replacement reactionequation: Sodium metal reacts withaqueous hydrochloric acid Na(s) + HCl(aq) Note: Sodium replaces thehydrogen ion in the reaction 39. Single ReplacementReactions Sodium chloride solid reacts withfluorine gas NaCl(s) + F2(g) Note that fluorine replaces chlorine in the compound Aluminum metal reacts withaqueous copper (II) nitrateAl(s)+ Cu(NO3)2(aq) 40. 4. Double-Replacement Two ionic compounds react byexchanging cations to form twodifferent compounds. Again, whether one metal willreplace another depends on theactivity series of metals chart.RS + TU RU + TS 41. Double Replacement Reactions Think about it like foiling in algebra,first and last ions go together + insideions go together Example: AgNO3(aq) + NaCl(s) AgCl(s) + NaNO3(aq) Another example: K2SO4(aq) + Ba(NO3)2(aq) 42. More on dbl replacement Takes place in aqueous solutions Usually produces a precipitate, gas, or molecular compound Aqueous solutions often disassociate (break apart) in water 43. Practice Predict the products. Balance theequation1. HCl(aq) + AgNO3(aq) 2. CaCl2(aq) + Na3PO4(aq) 3. Pb(NO3)2(aq) + BaCl2(aq) 4. FeCl3(aq) + NaOH(aq) 5. H2SO4(aq) + NaOH(aq) 6. KOH(aq) + CuSO4(aq) 44. 5. Combustion A hydrocarbon reacts withoxygen producing energy aslight and heat. Hydrocarbons are compoundscomposed of C, H, andsometimes O. Always forms carbon dioxideand water!!CHO + O2 CO2 + H2O 45. Combustion Reactions Products in combustionare ALWAYS carbondioxide and water.(although incompleteburning does cause someby-products like carbonmonoxide) Combustion is used toheat homes and runautomobiles (octane, asin gasoline, is C8H18) 46. Combustion ReactionsEdgar Allen Poesdrooping eyes andmouth are potentialsigns of COpoisoning. 47. Bellringer 10/18 Identify the following reactions as decomposition, combustion, single replacement, double replacement, or combination.1. T + RS TS + R2. CHO + O2 CO2 + H2O3. RS R + S4. Al + N2 AlN 48. Bellringer give the products1. T+ + RS 2. CHO + O2 3. RS 4. Al + N2 49. Total Ionic Equations Once you write the molecular equation(synthesis, decomposition, etc.), youshould check for reactants andproducts that are soluble or insoluble. We usually assume the reaction is inwater We can use a solubility table to tell uswhat compounds dissolve in water. If the compound is soluble (doesdissolve in water), then splits thecompound into its component ions If the compound is insoluble (does NOTdissolve in water), then it remains as acompound 50. Solubility Table 51. Solubilities Not on the Table! Gases only slightly dissolve in water Strong acids and bases dissolve inwater Hydrochloric, Hydrobromic, Hydroiodic, Nitric, Sulfuric, Perchloric Acids Group I hydroxides (should be on your chartanyway) Water slightly dissolves in water! (H+and OH-) For the homework SrSO4 is insoluble;BeI2 and the products are soluble There are other tables and rules thatcover more compounds than your table! 52. Total Ionic EquationsMolecular Equation:K2CrO4 + Pb(NO3)2 PbCrO4 + 2 KNO3Soluble Soluble Insoluble SolubleTotal Ionic Equation:2 K+ + CrO4 -2 + Pb+2 + 2 NO3- PbCrO4 (s) + 2 K+ + 2 NO3- 53. Net Ionic Equations These are the same as totalionic equations, but you shouldcancel out ions that appear onBOTH sides of the equationTotal Ionic Equation:2 K+ + CrO4 -2 + Pb+2 + 2 NO3- PbCrO4 (s) + 2 K+ + 2 NO3-Net Ionic Equation:CrO4 -2 + Pb+2 PbCrO4 (s) 54. Net Ionic Equations Shows the molecules brokenapartAgNO3(aq) + NaCl(aq) AgCl(s) + NaNO3(aq)vs.Ag+ + NO3- + Na+ + Cl- AgCl(s) + Na+ + NO3-Which ions are the same on both sides of the reaction?These are spectator ions! Na+ NO3-So, the Net equation is: Ag+ + Cl- AgCl 55. Net Ionic Equations Try this one! Write the molecular, totalionic, and net ionic equations for thisreaction: Silver nitrate reacts with Lead (II)Chloride in hot water.Molecular:Total Ionic:Net Ionic: 56. Compounds SolubilitySalts of alkali Solublemetals &ammoniaSolubilityNitrate salts Solubleand chloratesalts Precipitates formSulfate salts,Solublewhen an insolubleexceptcompoundssolid is formed.with Pb2+, Ag+,Hg22+, Ba2+, This can beSr2+, and Ca2+Chloride salts, Soluble predicted by usingexcept the solubility tablecompoundswith Pb2+, Ag+ on pg 344!and, Hg 2+ Not soluble = 2Carbonates, Most arephosphates,chromates,insolubleprecipitatesulfides, andhydroxides 57. Will a Precipitate Form?2AgNO3 + H2S Ag2S + 2 HNO3 (s) Yes salts with Ag are not soluble! The solid Ag2S will precipitate out! 58. Formation of a precipitate 59. Bellringer Using complete sentences tellthe difference between a netionic equation and a completeionic equation, then give anexample of each. 60. Recall!1. Write 1 characteristic about each of the 5 reactions discussed in class to help you remember that reaction. 61. Recall1. Comb/synth: two (single substances) reactants become one product2. Decomp: one reactant breaks into two products3. Combust: combines with O24. SR: Has 1 single ion plus a compound on reactants side5. DR: Has 2 compounds on reactants side 62. Exit What type of practice hashelped you best understandwriting and balancingequations?