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Unit 8 Chemical Equations and Reactions. Unit 8 Goals Describe evidence and characteristics of chemical reactions Write balanced chemical equations Identify.

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Presentation on theme: "Unit 8 Chemical Equations and Reactions. Unit 8 Goals Describe evidence and characteristics of chemical reactions Write balanced chemical equations Identify."— Presentation transcript:

1 Unit 8 Chemical Equations and Reactions

2 Unit 8 Goals Describe evidence and characteristics of chemical reactions Write balanced chemical equations Identify the types of reactions Determine if an ionic compound is soluble or insoluble in water Describe a precipitation reaction and relate it to solubility Predict if a precipitate will form or not using solubility rules Predict the products and balance molecular equations of precipitation reactions

3 Thinker: List observations that indicate a chemical reaction has taken place in the following situations: –A cut apple turns brown –An egg changes when it cooks –A log burns –A car rusts

4 Reminder: Chemical Reactions are indicated by: –Bubbling –Color change –Energy released as heat and light –Formation of solids Hallmark: –At least one chemical has changed its formula

5 Writing Reactions Several ways to write equations: –Always have reactants on left –Always have products on the right –Word Equations Methane + Oxygen Carbon Dioxide + Water –Formula Equation CH 4 + O 2 CO 2 + H 2 O –Balanced Formula Equations Well learn how to do this tomorrow CH 4 + 2O 2 CO 2 + 2H 2 O

6 Energy in Reactions Some reactions require energy –Endothermic –Bonds breaking overall –Ex: Dinitrogen tetroxide + energy nitrogen dioxide N 2 O 4 + energy NO 2

7 Energy in Reactions Other reactions make energy –Exothermic –Bonds created overall –Ex: Methane + Oxygen Carbon dioxide + Water + Energy CH 4 + O 2 CO 2 + H 2 O + energy

8 Symbols in Reactions Equations are like recipes (s) - solid (l) - liquid (g) - gas (aq) - aqueous (dissolved in water) - yields - reversible reaction - reactants are heated Pd, Mn, etc. - catalyst

9 Homework Reread p On p. 266 do SR 11-17

10 What is Wrong With These Reactions?

11 HW Answers (side 1) 1.NH 3 + HCl NH 4 Cl 2.CaCO 3 CaO + CO 2 3.BaO + H 2 O Ba(OH) 2 4.CH 3 CHO CH 4 + CO 5.Zn + Cu(NO 3 ) 2 Zn(NO 3 ) 2 + Cu 6.CaSO 3 CaO + SO 2 7.Fe + H 2 SO 4 FeSO 4 + H 2 8. C 2 H 6 N 2 C 2 H 6 + N 2 9. CO + Cl 2 COCl MnI 2 Mn + I 2

12 HW Answers (side 2) 11.N 2 O 5 + H 2 O HNO 3 12.Mg + TiCl 4 MgCl 2 + Ti 13.C + ZnO Zn + CO 2 14.Br 2 + NaI NaBr + I 2 15.PCl 3 + Cl 2 PCl 5 16.P + Br 2 PBr 3 17.CaH 2 + H 2 O Ca(OH) 2 + H 2 18.H 2 SO 4 + KOH K 2 SO 4 + H 2 O 19.C 3 H 8 + O 2 CO 2 + H 2 O 20.C 6 H 6 + O 2 CO 2 + H 2 O

13 Chemical Reactions: Conserve Mass –No mass is created –No mass is destroyed Therefore: –No atoms are created –No atoms are destroyed What happens? –Bonds (energy) are created, destroyed or rearranged

14 What does this mean? Formation of Water: H 2 + O 2 H 2 O The above equation is not correct! –It does not conserve matter. H – 2|H - 2 O – 2|O - 1 We need to balance the equation # of atoms at start = # of atoms at end

15 Balancing Equations Purpose: To show how much of each reactant is needed to make a certain quantity of product. What can we do? –Add coefficients to each formula Acts as a multiplier for that formula CO 2 2CO 2 2Ba(OH) 2 C – 1 C – 2 Ba – 2 O – 2 O – 4 O – 4 H – 4

16 General Rules for Balancing 1.Identify reactants & products –Write equation, predict products as necessary 2.Count atoms –Look for polyatomic ions 3.Insert coefficients –Balance one atom/polyatomic at a time –Delay balancing elements appearing in more than 1 formula on each side. –Do not rewrite formulas! –Do not change subscripts! –Odd-even technique 4.Verify your results

17 Example:

18 Lets try these Ca 2 Si + Cl 2 CaCl 2 + SiCl 4 –Ca 2 Si + 4Cl 2 2CaCl 2 + SiCl 4 P 4 + O 2 P 2 O 5 –P O 2 2 P 2 O 5 C 3 H 8 + O 2 CO 2 + H 2 O –C 3 H 8 + 5O 2 3CO 2 + 4H 2 O Is this correct? –2 P O 2 4 P 2 O 5

19 Homework: Balancing Chemical Equations Worksheet

20 Thinker: What do the following terms mean to you? –Synthesis –Decomposition –Displacement –Talk with others around you. –Compare definitions & examples.

21 Classifying Reactions Classified to help predict products Five Basic Types: –Synthesis –Decomposition –Single Displacement –Double Displacement –Combustion –... more, but beyond scope of this unit.

22 Combustion Often used to generate energy Gas, coal, starches, alcohol, sugars, cellulose, oil, etc. (has C compound) Ex: –CHX + O 2 H 2 O + CO 2 + energy –C 3 H 8 + 5O 2 3CO 2 + 4H 2 O + energy –CH 3 CH 2 OH + 3O 2 2CO 2 + 3H 2 O + energy

23 Synthesis Greek - to put together 2 or more formulas combine to form 1 formula Ex: –A + B AB –C + O 2 CO 2 –2C + O 2 CO –2Na + Cl 2 2NaCl 2 –CaO (s) + H 2 O (l) Ca(OH) 2(s)

24 Decomposition Opposite of synthesis Binaries usually elements Compounds 3+ usually elements Ex: –AB A + B –CaCO 3 CaO + CO 2 –2KClO 3 2KCl + 3O 2 –Mg(OH) 2 MgO + H 2 O –Air Bags: NaN 3(s) Na (s) + N 2(g)

25 Single Displacement A single atom replaces another in a compound. Like charges exchange places: –Metals replace metals or H –Nonmetals replace nonmetals Ex: –A + BC AC + B –2Al (s) + 3CuCl 2(aq) 2AlCl 3(aq) + Cu (s) –Cu (s) + AgNO 3(aq) CuNO 3(aq) + Ag (s)

26 Reactivity (Activity Series) Just because we put chemicals together will there be a reaction? –Not necessarilly –See the Activity Series (p.281 or Appendix A-9 p.832) More Rx elements will replace less Rx elements in compounds Ex: –K will replace H in H 2 O (forms KOH + H 2 ) –Cu will replace Ag in AgNO 3

27 Will the following React? Ag in Cu(NO 3 ) 2 Cu in AgNO 3 K in Mg(ClO) 2 Al in ZnCrO 4 Zn in Al 2 (CrO 4 ) 3 CuCl 2 containing Pb CuCl 2 containing Ag No Yes No Yes No

28 Double Displacement Similar to single displacement 2 reactants; 2 products Like charges exchange places Must result in: a solid, a gas, or a molecule Ex: –AB + YZ AZ + YB –2KI (aq) + Pb(NO 3 ) 2(aq) PbI 2(s) + 2KNO 3(aq) –BaO + H 2 O Ba 2 OH + H 2

29 Questions? Rx Type Flowchart on p 284 HW: –Read section 8-3 –S.R. 1-10

30 Thinker: What is a spectator? What role does a spectator play?

31 Writing Net Ionic Equations What is the purpose to outlining? –Summarizing important information How does this relate to spectators and reactions? Hint: –Are there any types of reactions where some things do not change (phase)? –Yes: Ionic Equations (1 & 2 displacement)

32 Ionic Compounds Dissolve in H 2 O Ions separate from each other Thus: –2KI (aq) + Pb(NO 3 ) 2(aq) PbI 2(s) + 2KNO 3(aq) Looks more like: –2K + (aq) + 2I - (aq) + Pb 2+ (aq) + 2(NO 3 ) - (aq) PbI 2(s) + 2K + (aq) + 2NO 3 - (aq)

33 But Wait! 2K + (aq) + 2I - (aq) + Pb 2+ (aq) + 2(NO 3 ) - (aq) PbI 2(s) + 2K + (aq) + 2NO 3 - (aq) This is too long to write. Lets outline the net equation. –What does net mean? Hint: What does net profit mean? –We can remove the spectator ions. Leaving us with: –2I - (aq) + Pb 2+ PbI 2(s)

34 Another Example: Single Displacement This Time Word Equation –Zinc + Copper (II) Sulfate Copper + Zinc Sulfate Formula Equation –Zn (s) + CuSO 4(aq) Cu (s) + ZnSO 4(aq) All Ions: –Zn (s) + Cu 2+ (aq) + SO 4 2- (aq) Cu (s) + Zn 2+ (aq) + SO 4 2- (aq) Net Ionic Equation: –Zn (s) + Cu 2+ (aq) Cu (s) + Zn 2+ (aq)


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