Chemical Reactions: evidence, writing them, balancing them Zumdahl Chapter 6 Notes Start Date: ______

Clues of Chemical Reactions 1.Color changes Ex: 2. Solid forms (precipitate) 3. Gas forms 4. Heat is produced or absorbed

Writing Chemical Equations Chemicals present before reaction are called: reactants, and are shown on the left side of the equation Chemicals present after the reaction are called: products, and are shown on the right side of the equation. ID the reactants and products (by name) in the following equation: CO2(g) + H2O(l)  H2CO3(aq)

Writing unbalanced chemical equations Look for key words that indicate whether the chemicals are reactants or products Reactant phrases A + B “react” A “decomposes” “to form” A “will produce” Z “when combined with B” Product phrases ...”to form Y and Z” …”to produce Y and Z” …”will result in formation of Z”

Try these out! Write the unbalanced chemical equation for each of the following reactions When barium peroxide is added to water, hydrogen peroxide and a precipitate of barium oxide forms. BaO2(aq) + H2O(l)  BaOH(s) If aqueous solutions of potassium chromate and barium chloride are mixed, a bright yellow solid (barium chromate) forms and settles out of the mixture, leaving potassium chloride in solution. K2CrO4(aq) + BaCl2(aq)  BaCrO4(s) + KCl(aq)

Balancing Chemical Equations The process of adding numerical coefficients in front of compounds in chemical equations to ensure that law of conservation of matter is satisfied. NEVER touch the numerical subscripts! Write the unbalanced form of the chemical reaction, including all states of matter subscripts Balance the rxn by putting in numerical coefficients as necessary

How to Balance Chem. Eq’ns Write the unbalanced equation w/subscripts Make a 2 x 2 T-table underneath the unbalanced equation In the first cell on left, write initial counts of reactants and circle to indicate compounds. Do the same with products 4. In the cells underneath initial counts, write overall counts, making symbols line up from reactants to products 5. Multiply by coefficients at the initial count bubbles level, and update final counts. Adjust as needed, and then record final coefficients. CH4(g) + O2(g)  CO2(g) + H2O(g) C: 1 O: 2 C: 1 H: 2 H: 4 O: 2 O: 1 C: 1 C: 1 H: 4 H: 2 O: 2 O: 3

Driving forces for chemical reactions   Formation of a solid Formation of a gas Formation of water Transfer of electrons

Chemical Reactions Oxidation-Reduction (redox) synthesis combustion synthesis R: CxHxOx + O2(g) P: CO2(g) + H2O(g) Met. + nmet. in el. form Nmet. + O2(g) in el. form

Chemical Reactions: Combustion In the flaming dollar bill combustion, ethanol (C2H6O) and oxygen gas combine to form carbon dioxide gas and water vapor. Write the full balanced equation for this reaction

Chemical Reactions: Combustion In the methane bubbles demonstration, we reacted methane gas (CH4) with oxygen gas to produce carbon dioxide gas and water vapor.

Chemical Reactions: Single Displacement and Synthesis In the “Filling and Popping a Balloon” reaction, zinc metal reacts with hydrochloric acid to form hydrogen gas and aqueous zinc (II) chloride. Write the full balanced equation. We then react the hydrogen gas with the oxygen gas to produce water vapor. Write the full balanced equation.

Gummy Bear Demise! In the gummy bear demise, we heated up the solid potassium chlorate to decompose the potassium chlorate into solid potassium chloride and oxygen gas. The oxygen gas then reacts with the sucrose in the gummy bear in a combustion reaction. Write the complete balanced equation for the potassium chlorate decomposition only.

Lights out. The conductivity apparatus is put into aqueous sulfuric acid light bulb lights A barium hydroxide solution is added drop by drop to the sulfuric acid solution to form water and a precipitate of barium sulfate  light bulb goes out Write the complete balanced equation for the reaction of aqueous barium hydroxide and aqueous sulfuric acid.

Types of Redox Reactions combustion – reaction between hydrocarbon (CxHxOx) and O2(g)  CO2(g) and H2O Synthesis – rxn b/w a metal and nonmetal in their elemental forms  ionic cmpd, or a rxn b/w a nonmetal and oxygen, both in elemental forms Decomposition – rxn where one cmpd breaks down into more than one simpler cmpd Single Displacement-A free element (usu. metal) displaces another element (usu. metal) from a compound (usu. ionic compound) A + BC  AC + B

Chemical Reactions Oxidation-Reduction (redox) synthesis combustion synthesis decomposition single displacement R: CxHxOx + O2(g) P: CO2(g) + H2O(g) Met. + nmet. in el. form Nmet. + O2(g) in el. form One R, more prod. A + BC  AC + B

Chemical Reactions: Decomposition In the “Elephant’s toothpaste” reaction, the decomposition of aqueous hydrogen peroxide is catalyzed by a solution of potassium iodide to create very hot water vapor and oxygen gas.

Redox Reactions- That’s where those ionic compounds come from! Redox reactions- involve the transfer of electrons 1 example: when a metal (in elemental form) reacts with a nonmetal (in elemental form)  Ionic compound this is what type of reaction? (synthesis) Transfer of e’s from the metal to the nonmetal.

Example Na(s) + Cl2(g)  2NaCl(s) reactant charges charges in compound produced Na 0 Na +1 Cl 0 Cl -1 1 electron(s) were transferred from Na to Cl LEOGER (loss of electrons = oxidation, gain of electrons = reduction)

Single Displacement and the Activity Series In order for A to displace B, A must be more reactive than B A + BC  AC + B Will this reaction occur? Predict the products: Li(s) + NaCl(aq)  Na(s) +LiCl(aq)

Classify each type of reaction and balance Cs(s) + Br2(l)  CsBr(s) synthesis: Cs(s) + Br2(l)  2CsBr(s) C2H2(g) + O2(g)  CO2(g) + H2O(l) combustion: C2H2(g) + 3O2(g)  2CO2(g) + 2H2O(l) PBr3(l)  P4(s) + Br2(l) decomposition: 4PBr3(l)  P4(s) + 6Br2(l)

Classify each type of Redox Reaction, predict the products, and balance each H2O2(l)  decomposition: 2H2O2(l)  2H2O(g) + O2(g) F2(g) + Ca(s)  synthesis: F2(g) + Ca(s)  CaF2(s) C2H4(g) + O2(g)  combustion: C2H4(g) + 6O2(g)  2CO2(g) + 2H2O(g)

Classify each type of Redox Reaction, predict the products, and balance each Fe(s) + CuSO4(aq)  Single displacement: Fe(s) + CuSO4(aq)  Cu(s) + FeSO4(aq) Cu(s) + FeSO4(aq)  Cu(s) + FeSO4(aq)  NO RXN (copper is not more reactive than iron)

Chemical Reactions Double Displacement Oxidation-Reduction (redox) precipitation acid-base P: one aq. Ionic cmpd, one solid ionic cmpd (precipitate) R: two aq. ionic cmpds combustion synthesis decomposition single displacement R: strong acid and strong base P: water and ionic cmpd (aq. or solid) R: CxHxOx + O2(g) P: CO2(g) + H2O(g) Met. + nmet. in el. form Nmet. + O2(g) in el. form One R, more prod. A + BC  AC + B

Double Displacement (DD) Reactions: precipitation and acid-base Because ionic compounds that dissolve in water separate into their cation and anion components (each surrounded by water): AB(aq) + CD(aq)  AD + CB the products can be: both aq. (no reaction) one aq. and one ppt. (precipitation) one aq. and one water (acid-base) one ppt. and one water. (acid-base)

Predicting the products of precipitation reactions Switch the cations and anions to predict products (make sure you consider charges and write cation first in each new formula) Predict the states of matter subscripts of products using solubility table (provided), if both aq. products, no reaction Soluble Insoluble Most NO3- Salts   Most salts of Na+, K+, and NH4+ Most chloride salts (Cl-) and iodide and bromide salts AgCl, PbCl2, Hg2Cl2,Those containing Ag, Hg, Pb Most sulfate (SO42-) salts BaSO4, PbSO4, CaSO4 NaOH and KOH Most hydroxide () compounds. Ba(OH)2 and Ca(OH)2 only moderately soluble Most sulfide (S2-) carbonate (CO32-) and phosphate (PO43-) salts

Let’s try some!! Predict the products of the following reactions, and then balance the equations (if a reaction occurs) FeSO4(aq) + KCl(aq)  FeSO4(aq) + KCl(aq)  NO REACTION (both aqueous prod.) FeCl3(aq) + H3PO4(aq)  FeCl3(aq) + H3PO4(aq)  3HCl(aq) + FePO4(s) (NH4)2S(aq) + CuCl2(aq)  (NH4)2S(aq) + CuCl2(aq)  2NH4Cl(aq) + CuS(s)

The complete ionic equation A complete ionic equation shows all aqueous ionic compounds separated into their ions Molec. eq’n: Pb(NO3)2(aq) + 2KI(aq)  PbI2(s) + 2KNO3(aq) Comp. ionic eq’n: Pb2+(aq) + 2NO3-(aq) + 2K+(aq) + 2I-(aq)  PbI2(s) + 2K+(aq) + 2NO3-(aq) Net ionic eq’n: Pb2+(aq) + 2I-(aq)  PbI2(s)

The net ionic equation A net ionic equations shows only the compounds directly participating in the reaction Comp. ionic: Pb2+(aq) + 2NO3-(aq) + 2K+(aq) + 2I-(aq)  PbI2(s) + 2K+(aq) + 2NO3-(aq) Net ionic eq’n: Pb2+(aq) + 2I-(aq)  PbI2(s)

Try these on your own Write the net ionic equation for the following reaction: BaCl2(aq) + Na2SO4(aq)  BaSO4(s) + 2NaCl(aq) Ba2+(aq) + SO42-(aq) BaSO4(s)

Keep going! What is the net ionic equation for the following reaction? (NH4)2SO4(aq) + CaCl2(aq)  2NH4Cl(aq) + CaSO4(s) Ca2+(aq) + SO42-(aq) +  CaSO4(s)

Acids and bases Acids produce H+ ions when dissolved in water (strong acids will donate all protons) Bases produce OH- ions when dissolved in water (strong bases will accept a proton for every OH-) H+ Cl- H+ Cl- H+ Cl- Na+ Na+ OH- Na+ OH- OH-

Reactions of Strong Acids and Strong Bases water is created when a strong acid reacts with a strong base Increasing Strength as go towards top Strong Acids Strong Bases HClO4 KOH HI Ba(OH)2 HBr CsOH HCl NaOH H2SO4 Sr(OH)2 HNO3 Ca(OH)2 LiOH RbOH

Determine the balanced molecular equation, the complete ionic equation, and the net ionic equation HNO3(aq) + KOH(aq)  b. mole. equation: HNO3(aq) + KOH(aq)  H2O(l) + KNO3(aq) com. ionic eq’n: H+(aq) + NO3-(aq) + K+(aq) + OH-(aq)  H2O(l) + K+(aq) + NO3-(aq) net. Ionic eq’n: H+(aq) + OH-(aq)  H2O(l)

hydrochloric acid plus sodium hydroxide  Determine the balanced molecular equation, the complete ionic equation, and the net ionic equation hydrochloric acid plus sodium hydroxide  HCl(aq) + NaOH(aq)  NaCl(aq) + H2O(l) Complete ionic equation: H+ (aq) + Cl-(aq) + Na + (aq) + OH-(aq)  Na + (aq) + Cl-(aq) + H2O(l) Net ionic equation: H+ (aq) + OH-(aq)  H2O(l)

Try some on your own! Solid barium peroxide is added to water to form aqueous hydrogen peroxide and a precipitate of barium oxide. Write then balance. BaO2(s) + H2O(l)  H2O2(aq) + BaO(s) Fe3O4(s) + CO(g)  Fe(s) + CO2(g) (disregard this one– it’s incorrect as written)