Chemical Reactions Balance Equation Double-displacement Reaction: Precipitation acid-base neutralization gas-evolving Single-displacement Reaction

Experiencing Chemical Change Chemical Reactions: happening both around you and in you all the time!  +  some are very simple, others are complex involving changes in the structures of the molecules  many times we can experience the effects of those changes Chemical reactions you experience? Combustion of gasoline/natural gas Seasonal color change of leaves Bleaching of laundry 2

Chemical Reactions Reactants  Products Chemical changes: New matter forms Rearrangement and exchange of atoms to produce new molecules Elements are not transmuted A reaction resemble life cycles (at 1:45) Reactants  Products 3

Chemical Equations: Conservation of Mass Matter cannot be created or destroyed Total mass cannot change Total mass of the reactants will be the same as the total mass of the products: Mass Reactant = Mass Product All the atoms present at the beginning are still present at the end: #Atom X (Reactant) = #Atom X (Product) if all the atoms are still there, then the mass will not change 4

Components in Chemical Equations: 2Mg(s) + O2(g) ® 2MgO(s) Shorthand way of describing a reaction Provides information about the reaction Formulas of Reactants (Left) and Products (Right) States of Reactants and Products in “( )”. (solid/liquid/gas) Relative #Reactant and #Product molecules (Coefficients) 5

Symbols Used in Equations Indicating the state after chemical (g) = gas; (l) = liquid; (s) = solid (aq) = aqueous = dissolved in water energy symbols used above the arrow for decomposition reactions D = heat hn = light shock = mechanical elec = electrical 6

Combustion of Methane: Balanced! To obey the Law of Conservation of Mass, the equation must be balanced CH4(g) + 2 O2(g) ® CO2(g) + 2 H2O(g) O C + O H + O + H C + 1 C + 4 H + 4 O 7

Balance Table CH4(g) + 2 O2(g) ® CO2(g) + 2 H2O(g) For a balanced equation, there are equal numbers of atoms of each element on the Reactant and Product sides to obtain the number of atoms of an element, multiply the subscript by the coefficient 1  C  1 4  H  4 4  O  2 + 2 8

How to Write & Balance Chemical Equation __CH4O(g) + __O2(g) ® __CO2(g) + __H2O(g) Skeletal equation Balance table: Polyatomic ions as one “Group”. 3. Pick an element to balance: Pick Element/Group w/ highest #Atoms Find the Least Common Multiple Multiply each count by a factor to equal the LCM. Recount and Repeat until Balanced. 9

Example Solid aluminum react with aqueous sulfuric acid to form aqueous aluminum sulfate and hydrogen gas Write a skeletal equation. Count #Atom or #Groups Setup balancing table and balance. Don’t start with elements in more than one formula Find the Least Common Multiple of the number of atoms on each side. 10

Example: Balance as Ions Fe(CN)3(s) + H2SO4(aq) ® Fe2(SO4)3(aq) + HCN(aq) ____ and ____ are groups 11

Example: Balance equation C8H18 + O2 ® CO2 + H2O 12

Practice: Balancing Equations C12H22O11 + O2  CO2 + H2 O (NH4)3PO4 + Ca(NO2)2  Ca3(PO4)2 + NH4NO2

Classifying Reactions A. based on the process that happens (we observes) precipitation, neutralization, formation of a gas, or transfer of electrons

Classifying Reactions B. by what the atoms and/or ions do (at molecular/atomic level) Type of Reaction General Equation Synthesis A + B  AB Decomposition AB  A + B Displacement A + BC  AC + B Double Displacement AB + CD  AD + CB

Predicting Whether a Reaction Will Occur in Aqueous Solution “Forces” that drive a reaction formation of a solid (aka “Precipitation”) formation of water formation of a gas transfer of electrons when chemicals (dissolved in water) are mixed and one of these 4 things can occur, the reaction will generally happen 16

Double Displacement Reactions Exchange ionic partners: AB + CD  AD + CB Example: Iron(III) nitrate + sodium sulfide  Iron(III) __________ + sodium __________ Double displacement reaction occurs when forming Precipitation Water (Acid-base neutralization reaction) Gas (one of the products to make a gas)

Reactions in Aqueous Solutions Often the chemicals we are reacting together are dissolved in water Aqueous solutions = mixtures of a chemical dissolved in water Dissolving the chemicals in water helps them to react together faster Water molecules separate the chemicals into individual molecules or ions The free floating particles collide more frequently so the reaction speeds up 18

Dissociation of Ionic Compound Dissociation: When ionic compounds dissolve in water, the anions and cations are separated from each other - however not all ionic compounds are soluble in water! When compounds containing polyatomic ions dissociate, the polyatomic group stays together as one ion 19

Dissociation of Ionic Compounds Potassium iodide  potassium cations and iodide anions: KI(aq)  K+ (aq) + I-(aq) Copper(II) sulfate  copper(II) cations and sulfate anions: CuSO4(aq)  Cu2+(aq) + SO42-(aq) K+ I- K I SO4 SO42- Cu Cu2+ 20

Polyatomic Ionic Compounds Ammonium sulfate  ammonium cations and sulfate anions (NH4)2SO4(aq)  2 NH4+(aq) + SO42-(aq) SO4 SO42- NH4+ NH4+ NH4+ NH4+ 21

Practice: How Ionic Compounds Dissociate? Ammonium phosphate Cobalt(III) sulfate Zinc bromide

Formation of Precipitation Depends on the Solubility of Ionic Compound a compound is soluble in a liquid if it dissolves in that liquid. It almost completely dissociate into ions. NaCl is soluble in water a compound is insoluble if a significant amount does NOT dissolve in that liquid. It essentially does NOT dissociate into ions. CaCO3(marble stone) is insoluble in water though there is a very small amount dissolved, but not enough to be significant

How to Predict the Solubility of Ionic Compound? Predicting whether a compound will dissolve in water is not easy Such knowledge comes through Experimentation: Do some Experiments to test whether a compound will dissolve in water Then develop some rules based on those experimental results we call this method the Empirical method 24

Solubility Rule. Part I Compounds that are Generally Soluble in Water Compounds Containing the following Ions are Generally Soluble Exceptions (insoluble when combined with ions on the left) Li+, Na+, K+, NH4+; H+ (most acids in this class) none NO3–, C2H3O2–, ClO4– None Cl–, Br–, I– Cu+, Ag+, Hg22+, Pb2+ (CISMILE) SO42– Ag+, Ca2+, Sr2+, Ba2+, Pb2+

Solubility Rule II Compounds that are Generally Insoluble Compounds Containing the following Ions are Generally Insoluble Exceptions (when combined with ions on the left the compound is soluble or slightly soluble) OH– (hydroxide, base) Li+, Na+, K+, NH4+, Ca2+, Sr2+, Ba2+ S2– (sulfide) 26

How to predict the solubility of an ionic compound using the previous table? Knowing how to use that table ALONE is generally sufficient to predict the solubility of ionic compound. Rule of Thumb: if the ionic compound of interest does NOT contain any of the listed ions, it is INSOLUBLE! Example: Ca3(PO4)2 if the ionic compound of interest contains BOTH the listed anion AND the cation as EXCEPTION, it is INSOLUBLE. Example: Hg2I2

Predict an Ionic Compound’s Solubility in Water: HgSO4 1. Check the cation: Is it Li+, Na+, K+, or NH4+? If YES  the compound will be soluble in water regardless of the anion! If NO  follow the rule for the anion (Table 7.2) 2. if a rule says the compounds are mostly soluble, then the exceptions are insoluble 3. but if a rule says the compounds are mostly insoluble, then the exceptions are soluble note: slightly soluble  insoluble

Practice: Are they Soluble in Water? FeCl3 Pb(C2H3O2)2 BaSO4 (NH4)3PO4 Generally Soluble Exceptions Li+, Na+, K+, NH4+; H+ none NO3–, C2H3O2–, ClO4– None Cl–, Br–, I– CISMILE SO42– Ag+, Ca2+, Sr2+, Ba2+, Pb2+

Insoluble Ionic Compounds do not Dissociate into Ions Insoluble Ionic compounds do not dissolve in water because the Coulombic force among the ions is too strong for water molecules to break down the compound. Therefore they do not dissociate into ions BaSO4(s)  Ba2+(aq) + SO42-(aq)

Precipitation Reactions When two soluble ionic compounds in aqueous solution mix, ion exchange will take place AB + CD  AC + DB if one of the products is insoluble in water, it will come out of solution as a precipitate

Precipitation Reactions The “Yellow Tornado”:http://www.youtube.com/watch?v=RE-dFN7U91M&feature=related Pb(NO3)2(aq) + 2 KI(aq)  2 KNO3(aq) + PbI2(s)

No Precipitate Formation = No Reaction KI(aq) + NaCl(aq)  KCl(aq) + NaI(aq) all ions still present (all products are soluble),  no reaction

Example: Write balanced equation between aqueous solution of sodium carbonate and aqueous solution of copper(II) chloride. Predict if precipitation forms. Write the formulas of the reactants Determine the ions present for each reactant Exchange the Ions Write the formulas of the products cross charges and reduce Balance the Equation Determine the solubility of each product Add “(s)” after the insoluble products and “(aq)” after the soluble products

Predict if a reaction will form precipitate BaBr2 + Na2SO4  BaSO4 + NaBr (NH4)3PO4 + Ca(NO3)2  Ca3(PO4)2 + NH4NO3 2 NaOH + CuSO4  Cu(OH)2 + Na2SO4 Generally Soluble Exceptions Li+, Na+, K+, NH4+; H+ none NO3–, C2H3O2–, ClO4– None Cl–, Br–, I– CISMILE SO42– Ag+, Ca2+, Sr2+, Ba2+, Pb2+

Acid + Base Salt + Water Acid-Base Reactions Also as Neutralization reactions : the Acid and Base neutralize each other’s properties H+ from the Acid + OH- from the base  Water Cation from the base + Anion from the acid  salt (spectator ions) Acid + Base Salt + Water 2 HNO3(aq) + Ca(OH)2(aq)  Ca(NO3)2(aq) + 2 H2O(l)

Example:- Write and Balance equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide Write the formulas of the reactants Determine the ions present for each reactant Exchange the ions, H+ combines with OH- to make H2O(l). Tip: write water as HOH Write the formulas of the products Balance the Equation (may be quickly balanced by matching the numbers of H and OH to make HOH) Determine the solubility of the salt Write an (s) after the insoluble products and a (aq) after the soluble products. Water exists as liquid, so (l) for water.

Gas-Evolving Reactions Some reactions form a gas directly From the ion exchange K2S(aq) + H2SO4(aq)  K2SO4(aq) + H2S(g) Other reactions form a gas by the decomposition of one of the products into a gas and water Step 1: Na2CO3(aq) + H2SO4(aq)  Na2SO4(aq) + H2CO3(aq) Step 2: H2CO3  H2O(l) + CO2(g) Overall reaction: Na2CO3(aq) + H2SO4(aq)  Na2SO4(aq) + H2O(l) + CO2(g)

Compounds that Undergo Gas Evolving Reactions Reactant Type Reacting With Ion Exchange Product Decompose? Gas Formed Example metalnS, metal HS acid H2S no K2S(aq) + 2HCl(aq)  2KCl(aq) + H2S(g) metalnCO3, metal HCO3 H2CO3 yes CO2 K2CO3(aq) + 2HCl(aq)  2KCl(aq) + CO2(g) + H2O(l) metalnSO3 metal HSO3 H2SO3 SO2 K2SO3(aq) + 2HCl(aq)  2KCl(aq) + SO2(g) + H2O(l) (NH4)nanion base NH4OH NH3 KOH(aq) + NH4Cl(aq)  KCl(aq) + NH3(g) + H2O(l)

Example: Write and Balance equation between an aqueous solution of sodium sulfite and an aqueous solution of nitric acid. Predict if precipitate or gas will form. Write the formulas of the reactants Determine the ions present when each reactant dissociates Exchange the Ions Write the formulas of the products Check to see either product H2S, or if either product decomposes into gas (H2CO3, H2SO3, NH4OH). Balance the Equation Determine the solubility of other product Write “(s)”, or “(aq)”, or “(l) for water, or “(g)” for each product if appropriate

Practice: Complete and Balance the following double-displacement Reactions; Predict whether the following reactions will form precipitate, gas, or neutralization (hint: predict the solubility of each compound) HNO3 + Al(OH)3  HCl + (NH4)2CO3  BaCl2 + (NH4)2CO3 

Beyond Double Displacement Rxns Precipitation, Acid-Base, and Gas-evolving reactions all involved exchanging the ions in the solution Oxidation-Reduction reactions : reactions involve transferring electrons from one atom to another – also known as redox reactions many of these reactions are not done by dissolving the reactants in water Examples: Reaction between elements, Single Displacement Reaction, Combustion Reaction

Reactions of Metals with Nonmetals (Oxidation-Reduction) metals react with nonmetals to form ionic compounds ionic compounds are solids at room temperature the metal loses electrons and becomes a cation the metal undergoes oxidation: Na  Na+ + e- the nonmetal gains electrons and becomes an anion the nonmetal undergoes reduction: Cl2+ 2e- 2 Cl- Overall Reaction: 2 Na(s) + Cl2(g)  2NaCl(s)

Single-Replacement Reactions Aka Single-Displacement Reaction: A reaction in which a more active element displaces another less active element in a compound. A + BC  AB + C When iron bar placed in copper(II) sulfate solution: Iron is corroded, copper metal appears, blue color (Cu2+ ion) fades. Fe(s) + CuSO4(aq) → FeSO4(aq) + Cu(s) Here ______ is more active than ____.

Aqueous Acid Displacements Metals that precede (H) in the activity series react with acids, and those that follow (H) do not react with acids. More active metals react with acid to produce hydrogen gas and an ionic compound. Fe(s) + 2 HCl(aq) → FeCl2(aq) + H2(g) Metals less active than (H) show no reaction. Au(s) + H2SO4(aq) → NR

Active Metals and Water A few metals are active enough to react directly with water. These are called active metals. They react with water to produce a metal hydroxide and hydrogen gas. 2 Na(s) + 2 H2O(l) → 2 NaOH(aq) + H2(g) Ca(s) + 2 H2O(l) → Ca(OH)2(aq) + H2(g)

Combustion Reactions Reactions in which O2(g) is a reactant are called Combustion Reactions Combustion reactions release lots of energy Combustion reactions are a subclass of Oxidation-Reduction reactions 2 C8H18(g) + 25 O2(g)  16 CO2(g) + 18 H2O(g)

Tro's Introductory Chemistry, Chapter 7 Combustion Products to predict the products of a combustion reaction, combine each element in the other reactant with oxygen Reactant Combustion Product contains C CO2(g) contains H H2O(g) contains S SO2(g) contains N NO(g) or NO2(g) contains metal M2On(s) Tro's Introductory Chemistry, Chapter 7

Combination Reactions also known as Composition or Synthesis reactions Two (or more) reactants combine together to make one product simpler substances combining together 2 CO + O2 ® 2 CO2 CaO + H2O ® Ca(OH)2 2H2 + O2 ® 2H2O Tro's Introductory Chemistry, Chapter 7

Decomposition Reactions ONE large molecule is broken apart into smaller molecules or its elements caused by addition of energy into the molecule From one reactant, make 2 or more products Tro's Introductory Chemistry, Chapter 7

Practice: Write and Balance Word Equations iron(III) chloride + copper metal  iron(II) chloride + copper(II) chloride nitrogen gas + magnesium metal  magnesium nitride zinc phosphate + hydrochloric acid  phosphoric acid + zinc chloride

Determine if Each of the Following is Soluble in Water KOH Soluble, because the cation is K+ AgBr Insoluble, even though most compounds with Br- are soluble, this is an exception CaCl2 Soluble, most compounds with Cl- are soluble Pb(NO3)2 Soluble, because the anion is NO3- SrSO4 Insoluble, even though most compounds with SO42- are soluble, this is an exception

Write the formulas of the reactants Example: When an aqueous solution of sodium carbonate is added to an aqueous solution of copper(II) chloride, a white solid forms Write the formulas of the reactants Na2CO3(aq) + CuCl2(aq)  Determine the ions present when each reactant dissociates (Na+ + CO32-) + (Cu2+ + Cl-)  Exchange the Ions (Na+ + CO32-) + (Cu2+ + Cl-)  (Na+ + Cl-) + (Cu2+ + CO32-)

Write the formulas of the products Example: When an aqueous solution of sodium carbonate is added to an aqueous solution of copper(II) chloride, a white solid forms Write the formulas of the products cross charges and reduce Na2CO3(aq) + CuCl2(aq)  NaCl + CuCO3 Balance the Equation Na2CO3(aq) + CuCl2(aq)  2 NaCl + CuCO3

Na2CO3(aq) + CuCl2(aq)  2 NaCl(aq) + CuCO3(s) Example - When an aqueous solution of sodium carbonate is added to an aqueous solution of copper(II) chloride, a white solid forms Determine the solubility of each product NaCl is soluble CuCO3 is insoluble Write an (s) after the insoluble products and a (aq) after the soluble products Na2CO3(aq) + CuCl2(aq)  2 NaCl(aq) + CuCO3(s)

(H+ + NO3-) + (Ca2+ + OH-)  (Ca2+ + NO3-) + HOH(l) Example:- Write and Balance equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide Write the formulas of the reactants HNO3(aq) + Ca(OH)2(aq)  Determine the ions present when each reactant dissociates (H+ + NO3-) + (Ca2+ + OH-)  Exchange the ions, H+ combines with OH- to make H2O(l). Tip: write water as HOH (H+ + NO3-) + (Ca2+ + OH-)  (Ca2+ + NO3-) + HOH(l)

Write the formulas of the products Example: Write the molecular equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide Write the formulas of the products cross charges and reduce HNO3(aq) + Ca(OH)2(aq)  Ca(NO3)2 + HOH(l) Balance the Equation may be quickly balanced by matching the numbers of H and OH to make HOH coefficient of the salt is always 1 2 HNO3(aq) + Ca(OH)2(aq)  Ca(NO3)2 + 2 HOH(l)

Example 7.11 - Write the molecular equation for the reaction of aqueous nitric acid with aqueous calcium hydroxide Determine the solubility of the salt Ca(NO3)2 is soluble Write an (s) after the insoluble products and a (aq) after the soluble products 2 HNO3(aq) + Ca(OH)2(aq)  Ca(NO3)2(aq) + 2 H2O(l)

(Na+ + SO3-) + (H+ + NO3-)  (Na+ + NO3-) + (H+ + SO32-) Example - When an aqueous solution of sodium sulfite is added to an aqueous solution of nitric acid, a gas evolves Write the formulas of the reactants Na2SO3(aq) + HNO3(aq)  Determine the ions present when each reactant dissociates (Na+ + SO32-) + (H+ + NO3-)  Exchange the Ions (Na+ + SO3-) + (H+ + NO3-)  (Na+ + NO3-) + (H+ + SO32-)

Example - When an aqueous solution of sodium sulfite is added to an aqueous solution of nitric acid, a gas evolves Write the formulas of the products cross charges and reduce Na2SO3(aq) + HNO3(aq)  NaNO3 + H2SO3 Check to see either product H2S - No Check to see of either product decomposes – Yes H2SO3 decomposes into SO2(g) + H2O(l) Na2SO3(aq) + HNO3(aq)  NaNO3 + SO2(g) + H2O(l)

Example - When an aqueous solution of sodium sulfite is added to an aqueous solution of nitric acid, a gas evolves Balance the Equation Na2SO3(aq) + 2 HNO3(aq)  2 NaNO3 + SO2(g) + H2O(l) Determine the solubility of other product NaNO3 is soluble Write an (s) after the insoluble products and a (aq) after the soluble products Na2SO3(aq) + 2 HNO3(aq)  2 NaNO3(aq) + SO2(g) + H2O(l)

Practice: Complete and Balance the following Word equations copper(II) nitrate + sodium carbonate silver acetate + ammonium chloride potassium carbonate + phosphoric acid barium hydroxide + sulfuric acid

Practice: Complete and Balance the following Word equations copper(II) nitrate + sodium carbonate silver acetate + ammonium chloride potassium carbonate + phosphoric acid barium hydroxide + sulfuric acid Cu(NO3)2(aq) + Na2CO3(aq)  2 NaNO3(aq) + CuCO3(s) AgC2H3O2(aq) + NH4Cl(aq)  AgCl(s) + NH4C2H3O2(aq) 3K2CO3(aq) + 2H3PO4(aq)  2K3PO4(aq) + 3H2O(l) + 3CO2(g) Ba(OH)2(aq) + H2SO4(aq)  BaSO4(s) + 2 H2O(l)