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Chapter 8 Chemical Reactions

Chapter 8 Chemical Reactions. Balancing Equations & Types of Chemical Reactions GCC CHM 130. 8.1 Chemical Reactions. Is this a chemical or physical change?. Phys. Is this a chemical or physical change?. Chem. What are four signs a chemical reaction may have occurred?.

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Chapter 8 Chemical Reactions

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  1. Chapter 8 Chemical Reactions Balancing Equations &Types of Chemical Reactions GCC CHM 130

  2. 8.1 Chemical Reactions Is this a chemical or physical change? Phys Is this a chemical or physical change? Chem What are four signs a chemical reaction may have occurred? 1 A precipitate forms 3 Energy is released or absorbed 2 A gas forms w/o heating 4 A permanent color change

  3. Review • What is the difference between a chemical change (reaction) and a physical change? A physical change does NOT change the molecule – no bonds are broken, often just the state of matter changes. A chemical reaction DOES change the molecule into a different one.

  4. 8.2 Chemical Reactions • Reactants g Products • Balanced – same atoms on both sides • Remember to include physical states • (s) = solid • (l) = liquid • (g) = gas • (aq) = aqueous solution (dissolved in water)

  5. 8.3 Remember • Which elements are solid, liquid, gas • Which are diatomic • Matter can not be created or destroyed so reactions must be balanced • Subscripts tell how many atoms in that molecule H2O • Coefficients tell how many molecules 3 H2O

  6. Write the balanced chemical reaction A = Blue B = Red 3 A2 + B2g 2 A3B

  7. Draw and Balance These N2 (g) + H2 (g)  NH3 (g) H2 (g) + Br2 (l)  HBr (g) CO (g) + O2 (g)  CO2 (g)

  8. N2 (g) + 3 H2 (g)  2 NH3 (g)H2 (g) + Br2 (l)  2 HBr (g) 2 CO (g) + O2 (g)  2 CO2 (g)

  9. How to Balance a Rxn 1. Write the unbalanced chemical reaction with proper formulas first Ex: Sodium reacts with chlorine to produce solid sodium chloride. Na (s) + Cl2 (g) g NaCl (s) Why Cl2 not just Cl??? Cl is diatomic !!! Diatomic is only when elements are alone, does not apply to compounds. If Cl is diatomic, why not NaCl2?

  10. 2. Now change the coefficientsnever the subscripts till balanced. Count polyatomic ions as a group, don’t count the atoms. Answer: 2 Na (s) + Cl2 (g) g 2NaCl (s)

  11. Why can’t we change the subscripts? Write the reaction:Hydrogen reacts with oxygen to form water vapor. H2 (g) + O2 (g) g H2O (g) Now balance and use the lowest possible numbers. (Like reducing a number)

  12. You FIRST write the reaction with PROPER FORMULAS, once that is done you can NOT change the subscripts. Then you can balance by adding coefficients.

  13. Writing a reaction from words • Write then balance the reaction of phosphorus being heated with oxygen gas to make solid diphosphorus pentaoxide. P (s) + O2(g) g P2O5(s) 4 P (s) + 5 O2(g) g 2 P2O5(s) There are many in the end of chapter problems like this to practice.

  14. Hard Practice Prob – do at homeI’ll give answers next class (remind me) • Write then balance this reaction: aqueous nickel(III) sulfate plus lead(II) nitrate produces nickel(III) nitrate and solid lead(II) sulfate Ni2(SO4)3 (aq) + Pb(NO3)2 (aq) g Ni(NO3)3 (aq) + PbSO4 (s) Ni2(SO4)3 (aq) + 3 Pb(NO3)2 (aq) g 2 Ni(NO3)3 (aq) + 3 PbSO4 (s)

  15. 8.4 Types of Chemical Reactions 8.5 Combination Reactions: 2 reactants form one product A + X g AX 8.6 Decomposition: one reactant forms 2 or more products AX g A + X Combustion: burning with O2 to form carbon dioxide and steam CxHy + O2(g) g CO2 (g) + H2O (g) 8.8 Single Replacement: metal A becomes part of an ionic cmpd A + BX g AX + B 8.10 Double Replacement Reactions: switch partners AX (aq) + BY (aq) g AY (aq) + BX (s) 8.11 Neutralization Reactions: acid + base form water and salt HA(aq) + MOH(aq) g H2O (l) + MA(aq)

  16. 8.5 Combination Reactions Balance: P (s) + O2 (g) → P2O4 (g) 2 P (s) + 2 O2 (g) → P2O4 (g) 8.6 Decomposition Reactions Balance: Fe2O3 (s) → Fe (s) + O2 (g) 2 Fe2O3 (s) → 4 Fe (s) + 3 O2 (g)

  17. Combustion Reactions Write then balance the combustion of Propane gas, C3H8 C3H8 (g) + O2 (g) g CO2 (g) + H2O (g) C3H8 (g) + 5 O2 (g) g 3 CO2 (g) + 4 H2O (g)

  18. Combustion Reactions We are only doing simple hydrocarbon (CxHy) combusion reactions. So… Products are always CO2(g) + H2O(g) And O2(g) is always a reactant You should be able to predict the products for these !!!

  19. 8.7 Activity Series • Given to you on Periodic Table • Most active WANTS to be cation (+ charge) in compound with a buddy (social) • Least active WANTS to be alone as neutral element metal with zero charge (loner)

  20. 8.9 Solubility Rules Solubility Rules • Generally soluble compounds with: • Li+, Na+, K+, NH4+(ALWAYS!) • C2H3O2-, • NO3- • Halide ions (X), Cl-, Br-, I- • - BUT AgX, Hg2X2, HgX, PbX2insoluble • SO42- • - BUT SrSO4, BaSO4, • , PbSO4 are all insoluble • Generally insoluble compounds with: • CO32- • CrO42- • PO43- • S2- • - BUT CaS, SrS, BaSsoluble • OH- • - BUT Ca(OH)2, Sr(OH)2, and • Ba(OH)2soluble Soluble means dissolves in water. NaCl(aq) which is Na+ and Cl- ions in water Insoluble means does not or very little dissolves in water. AgCl(s)

  21. Drawings! Draw these chemicals in beakers of water. LiNO3 MgS Ca(OH)2 KI BaCO3

  22. Soluble is (aq), insoluble is (s)Write (aq) or (s) by each. Al(OH)3 Ca(NO3)2 K2S Li3PO4 Ba(C2H3O2)2 Sr(OH)2 (NH4)2CO3 PbI2 CuS (aq) (aq) (s) (aq) (aq) (aq) (s) (s) (aq) Now for practice let’s NAME these compounds!

  23. Electrolytes • Electrolytes are solutions that contain ions • Strong electrolytes are good conductors, ionic compounds that are soluble (completely dissolves into ions) are these. You will learn later that strong acids and bases are strong electrolytes. • Weak electrolytes are weak conductors, ionic compounds that are insoluble are these. Insoluble = only a few dissolve into ions. You will learn later that weak acids and bases are weak electrolytes. • Non-electrolytes are solutions that do not conduct at all, zero ions. Covalent chemicals are often non-electrolytes. • http://www.youtube.com/watch?v=1XWnovm6JLs&feature=related

  24. 8.8 Single Replacement Reactions • Look at the two metals or H, which is more active? • Most active wants to be in compound, if it already is then No Reaction (NR), if not switch partners. • Write the correct product formulas – the elemental state is always charge 0 • Write the states for the products. (s, l, g, aq) • Last is balance. Zn(NO3)2 (aq) + Na (s) → ? Zn(NO3)2 (aq) + 2 Na (s) → 2 NaNO3 (aq) + Zn (s) Na is +1 and NO3 is –1 so they already balance out, don’t need 2 Why not Na(NO3)2???

  25. Solid Metal + Acid If a metal is more active than H, then H2 gas produced. (You must write the products 1st, then the states, then balance last) Al (s) + HCl (aq) g ? Al (s) + HCl (aq) g AlCl3 (?) + H2 (?) Al (s) + HCl (aq) g AlCl3 (aq) + H2 (g) 2 Al (s) + 6 HCl (aq) g 2 AlCl3 (aq) + 3 H2 (g)

  26. Active Metals http://video.google.com/videoplay?docid=-3103610687149839311# http://www.youtube.com/watch?v=OFG4Yr7lQzw Active Metals Series: Li > K > Ba > Sr > Ca > Na The six active metals will react with water to produce hydrogen gas and the metal hydroxide. M (s) + H2O (l) → H2 (g) + MOH Write the reaction and balance (You must write the products 1st) 1. Cu (s) + H2O(l) g NR 2. Ba (s) + H2O(l) g 2 H2 (g) + Ba(OH)2 (aq)

  27. 17.1 Oxidation and Reduction • Single Replacement reactions are a type of REDOX reaction where oxidation and reduction occur. (Note you can’t have one without the other)

  28. Oxidation Numbers • Ox # = fancy name for charge • All elements in natural state = 0 • When in a compound, charge is + for metals and – for nonmetals depending on how many electrons lost or gained • Variable charge metals range from +1 to +9 in rare cases. Nomenclature worksheet has this info online Review CHARGES!!! http://web.gccaz.edu/~ksmith8/rev130.htm

  29. 17.2 Oxidation • Losing electrons, charge goes ______________ • Cu(s) g Cu2+ (aq) + 2 e- • Solid Cu is oxidized (OX = UP) • What is oxidized = reducing agent • What elements like to lose electrons? UP metals

  30. Reduction DOWN • Gaining electrons, charge goes ______________ • S (s) + 2 e-g S2- (aq) • Solid sulfur is reduced • What is reduced = oxidizing agent • What elements like to gain electrons? nonmetals

  31. Redox Reactions • Must have one chemical oxidized AND another reduced. Can’t have one w/o the other. • What is oxidized and reduced are always reactants, the products are the result of the redox. • So if asked “what is ox or red?”, answer is reactant chemicals. • When you answer, answer the whole compound, not just the element thatchanged charges. • You have to figure out the charges!!!

  32. Easy example Cu+2 (aq) + Fe(s) g Cu(s) + Fe+2(aq) Cu went from +2 to 0 so charge down = reduced Fe went from 0 to +2 so charge up = oxidized What is oxidized? What is reduced? What is oxidizing agent? What is reducing agent? Fe (s) Cu+2 (aq) Cu+2(aq) Fe(s)

  33. What is oxidized, reduced, ox agent, and red agent??? Co(NO3)3 (aq) + Pt (s) g Pt (NO3)3 (aq) + Co(s) • Co charge went from +3 to 0 • Pt charge went from 0 to +3 • So Co(NO3)3 is reduced (cobalt(III) nitrate) • Pt(s) is oxidized • Co(NO3)3 is oxidizing agent • Pt(s) is reducing agent

  34. What is oxidized, reduced? What is the ox agent, red agent? Ca(s) + NiCl2 (aq) g CaCl2(aq) + Ni(s) Ox = solid Ca NOT Ca2+ or CaCl2 Red = NiCl2 (aq) for fun what is the name? Ox Agent = NiCl2 (aq) Red Agent = Ca(s) (nickel(II) chloride) Do the redox practice problems in the online notes !!! AND there is a worksheet online for redox.

  35. 8.10 Double Replacement Reactions Precipitation is a type of DR Rxn and a solid forms AX (aq) + BY (aq) → AY (s) + BX (aq) Identify the solid then balance. 1. Ba(NO3)2 (aq) + MgSO4 (aq) → BaSO4 + Mg(NO3)2 (s) (aq) 2. Pb(NO3)2 (aq) + KI (aq) → PbI2 + KNO3 2 (s) 2 (aq) 3. BaCl2 (aq) + AgNO3 (aq) → Ba(NO3)2 + AgCl 2 (aq) 2 (s)

  36. 8.11 Neutralization Reactions Another type of DR Reaction HA + MOH → H2O + MA Products are usually water and ionic compound. Base Acid Write the products, the states, and THEN balance. HCl (aq) + Ba(OH)2 (aq) g 2 H2O (l) + BaCl2 (aq) 2 H3PO4 (aq) + Ca(OH)2 (aq) g 2 3 Ca3(PO4)2 (s) + 6 H2O (l)

  37. Summary • Know how to use solubility rules and draw ionic compounds in beakers of water • Recognize strong vs weak electrolytes • Recognize and balance • Combination • Decomposition • Double displacement - precipitation • Recognize, write products, and balance • Single displacement • Acid base neutralization • Combustion • Identify what is oxidized, reduced and the agents in a redox reaction

  38. You REALLY should do the worksheets for chapter 8 on the Worksheet websitehttp://web.gccaz.edu/~ksmith8/rev130.htm

  39. Self Tests • Page 230 Ch. 8 Try 1-5, 7-9, 11-16 • Page 510 Ch. 17 Try 1-2 • Answers in Appendix J

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