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Chemical Equations Ch.11

Chemical Equations Ch.11. Ch.11 Chemical Equations & Reactions. Sect.11-1 “Chemical Reactions” Chemical Rn : __________________________ ___________________________________ ___________________________________ Reminder: Substances before reaction = ___________

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Chemical Equations Ch.11

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  1. Chemical Equations Ch.11

  2. Ch.11 Chemical Equations & Reactions Sect.11-1 “Chemical Reactions” Chemical Rn: __________________________ ___________________________________ ___________________________________ Reminder: Substances before reaction = ___________ Substances after reaction = ___________

  3. Signs that a chemical rn has occurred: 1.) _________:Does rn produce or absorb heat? 2.) ________:Does rn produce light? Note: Heat/Light is not proof positive that a rn has occurred. 3.) _____________:Bubbles form in the rn. 4.) _______________:when 2 liquid solnsare combined and a solid is produced – solid is known as a ___________.

  4. Characteristics of a Chemical Eqn. 1.) Eqn needs to _______________________. 2.) Need _________________ for reactants and products. 3.) Law of Conservation of Mass holds. i.e. total mass before = total mass after or more importantly: _________________________________

  5. Word Eqns It’s easier to write an eqn by first writing it in words – __________. It is qualitative because no numbers are used. e.g. __________ + _________ →_________ __________ + Hydrogen →__________ where “+” means “reacts with” and is read as “and” “→” means “yields” or “produces” and is read as such.

  6. Next step: Convert the words into formulas, called a “Formula Equation” e.g. Hydrogen + Oxygen → Water ___ + ____→____ Nitrogen + Hydrogen → Ammonia ___ + ____→_____ (examples of formulas vs symbols?) Elemental Gases – F2, Cl2,… Liquids – Br2, Solid Metals – Na, Mg, Ca… Solid Non-Metals – S8, P4, I2.

  7. Last step: Balance the equation to create a “Balanced chemical equation” i.e. the # of each type of element before = after e.g. Hydrogen + Oxygen → Water H2 + O2→ H2O 2 H atoms 2 H atoms 2 O atoms 1 O atom Therefore need to balance. e.g. Nitrogen + Hydrogen → Ammonia N2 + H2 → NH3 2 N atoms + 2 H atoms ≠ 1 N atom and 3 H atoms Therefore need to balance.

  8. Trick: _______________________________ _______________________________. e.g.1: H2 + O2→ H2O (H is OK, now look at O) H2 + O2→2H2O (O is fixed, but H is now unbalanced. (Cannot fix H2O by changing it to H2O2 because you are changing the actual formula. Coefficient multiplies everything after it.) 2H2 + O2→2H2O (H and O are now balanced) i.e. # H before (4) = # H after (4) # O before (2) = # O after (2)

  9. e.g.2 N2 + H2 → NH3(balance the N) N2 + H2→2NH3 (now, balance the H) N2 + 3H2→2NH3(double check) # N atoms (2) before = # N atoms (2) after # H atoms (6) before = # H atoms (6) after Balanced Example: CH4 + O2→ CO2 + H2O Example: C3H8 + O2→ CO2 + H2O (other examples) BaCl2+ AlN Ba3N2 + AlCl3

  10. Balancing tricks / hints: • Balance the elements one at a time • First balance the atoms of the elements that are combined and that only appear once on each side of the equation • Treat polyatomic ions that appear on both sides of the equation, as single units e.g. _Al2(SO4)3 + _Ca(OH)2→ _Al(OH)3 + _CaSO4 • Balance the H & O atoms last • If you have a Hydroxide (OH) on one side, and water (H2O) on the other side, then treat H2O as H(OH). e.g.Ca + H2O  Ca(OH)2 + H2

  11. Other symbols used in Chemical equations: • solid e.g. NaCl(s) • liquid e.g. H2O(l) • gas e.g. CH4(g) (aq) aqueous – dissolved in water e.g. NaCl(aq)  precipitate (solid) is formed e.g. AgCl(s)  gas is formed (bubbles) e.g. H2(g) heat used/required catalyst reversible reaction (or  ) (do examples with above symbols) H2O2(aq) H2(g) + O2(g) ∆ KMnO4 KMnO4

  12. Magnesium metal is placed into a solution of Iron (III) Chloride to produce solid Iron and Magnesium Chloride solution. Word Eqn: . Formula Eqn: (Balanced) Chemical Eqn:

  13. Ethane (C2H6) gas burns in air to produce Carbon Dioxide gas and water vapor. Word Eqn: Formula Eqn: (Balanced) Chemical Eqn:

  14. Types of Reactions: • Synthesis Rn: (aka Composition rns) - aka direct combination rn. Where ____________________ to form a new compound. Generalized by: __________________ e.g. 2H2(g) + O2(g)→ 2H2O(g) e.g. Mg(s) + Cl2(g)→ MgCl2(s) Most metals react with O & S to produce Oxides & Sulphides. e.g. 2Mg(s) + O2(g)→ 2MgO(s) e.g. 8Ba(s) + S8(s)→ 8BaS(s)

  15. Non Metals react with Oxygen to produce Oxides e.g. S8(s) + 8O2(g)→ 8SO2(g)SulphurDiOxide e.g. C(s) + O2(g)→ CO2(g) Carbon DiOxide e.g. 2H2(g) + O2(g)→ 2H2O(g) Hydrogen Oxide(?) Active metal oxides react with H2O to produce metal hydroxides. e.g. Na2O(s) + H2O(l)→ 2NaOH(s) or (aq)?

  16. 2) DeComposition Reactions: -a ______________________ (breaks down) into 2 or more simpler substances. Usually requires an input of Energy. (Heat, electricity..) Generalized by: __________________ e.g. 2H2O(l)electricity 2H2(g) + O2(g) (Electrolysis) e.g. 2HgO(s)∆ or Heat 2Hg(l) + O2(g) e.g. H2O2(l)KMnO4 H2(g) + O2(g)

  17. 3) Single Replacement reactions: • where ___________________________ ____________________: Generalized by: A + BX → AX + B m m nm mnm m Or Y + BX → BY + X nm m nm m nm nm Rns usually need to take place _____________

  18. Examples: Mg(s) + AgNO3(aq) → Cl2(g) + NaBr(aq)→ Note: Just because you can write a chemical rn, it doesn’t mean that it will happen. We need to consult the __________________ • a list of elements organized according to how reactive they are. (see p.333 & handout) ___________________________________________________________________________________________________________________________ Same goes if Y is higher than X on the list. ( Do examples )

  19. 4) Double Replacement Rns: • where _______________________________ _____________________________. Generalized by: AX(aq) + BY(aq)→ AY + BX m nm m nm m nm m nm In order for a double replacement rn to occur, one of the products must be a: • ______________ (solid), or • _________, or • _______ [remember: H+ + OH-→ HOH (H2O)]

  20. If products do not contain one of the previous 3, then rn will not occur. Examples: Precipitate: (need to look at Appendix:B, Table B-9 on p.R54) KI(aq) + Pb(NO3)2(aq)→ Gas: FeS(s) + HCl(aq)→ Water: HCl(aq) + NaOH(aq)→

  21. 5.) Combustion Rns: • Is when a ______________________ (in the air) releasing a large amount of energy in the form of light, heat and sometimes sound. *If the substance is a HydroCarbon(CXHY) or an Alcohol (CXHY-1OH) then _______________ ________________ which we will focus on mostly. e.g. C2H6(g) + O2(g)→ Ethane C2H5OH(l) + O2(g)→ Ethanol

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