3Chemical ReactionsProcess in which one or more pure substances are converted into one or more different pure substancesReactants: Zn + I2Product: Zn I2
4Indications of a Reaction Temperature ChangeColor ChangeProduction of gasFormation of a precipitateProduction of light
54 Al(s) + 3 O2(g) ---> 2 Al2O3(s) Chemical Equations4 Al(s) O2(g) ---> 2 Al2O3(s)Reactants react to produce productsThe letters (s), (g), (l), and (aq) are the physical states of compounds.“aq” represents aqueous meaning dissolved in water (solution)The numbers in the front are called coefficients.Subscripts represent the number of each atom in a compound(Reactants)(Products)
6Chemical Reactions + → ↔ ↑ ↓ ∆ Meaning SymbolMeaning+used to separate one reactant or product from another→used to separate the reactants from the products - it is pronounced "yields" or "produces" when the equation is read↔used when the reaction can proceed in both directions - this is called an equilibrium arrow and will be used later in the course↑an alternative way of representing a substance in a gaseous state↓an alternative way of representing a substance in a solid state∆indicates that heat is applied to make the reaction proceed
7BrINClHOF! Diatomic Elements Elements that cannot exist by themselves (always occur in pairs)Bromine (Br2)Iodine (I2)Nitrogen (N2)Chlorine (Cl2)Hydrogen (H2)Oxygen (O2)Fluorine (F2)BrINClHOF!
8Writing Equations Practice 1. When lithium hydroxide pellets are added to a solution of sulfuric acid, lithium sulfate and water are formed.2 LiOH(s) + H2SO4(aq) Li2SO4(aq) + 2 H2O(l)2. When crystalline C6H12O6 is burned in oxygen, carbon dioxide and water vapor are formed.C6H12O6(s) + 6 O2(g) 6 CO2(g) + 6 H2O(g)
9Balancing Equations 2HgO(s) ---> 2 Hg(l) + O2(g) Law of Conservation of MassMatter cannot be destroyed (atoms of reactants must equal products)Balance equations to get same number of each atom on the left and right in an equation2 Hg atoms, 2 O atoms Hg atoms, 2 O atoms2HgO(s) ---> 2 Hg(l) + O2(g)
116 Types of Reactions Synthesis (combination) Decomposition Single Replacement (displacement)Double Replacement (precipitation)CombustionAcid-Base Neutralization
12Synthesis (Combination) Reactions Two or more substances combine to form a new compound.A + X AXSynthesis of:Binary compounds H2 + O2 H2OMetal carbonates CaO + CO2 CaCO3Metal hydroxides CaO + H2O Ca(OH)2Metal chlorates KCl + O2 KClO3Oxyacids CO2 + H2O H2CO3
13Decomposition Reactions A single compound breaks down into two or more simpler substancesAX A + XDecomposition of:Binary compounds H2O H2 + O2Metal carbonates CaCO3 CaO + CO2Metal hydroxides Ca(OH)2 CaO + H2OMetal chlorates KClO3 KCl + O2Oxyacids H2CO3 CO2 + H2O
14Single Replacement (displacement) Reactions One element replaces another in a reactionMetals replace metalsNonmetals replace nonmetalsA + BX AX + BBX + Y BY + X
15Activity Series Decide whether or not one element will replace another Metals can replace other metals provided that they are above the metal that they are trying to replaceIf the metal is not above what it is trying to replace, the result is “no reaction”
16Double Replacement (Precipitation) Reactions Two elements or ions “switch partners”AX + BY AY + BXOne of the compounds formed is usually a precipitate, an insoluble gas that bubbles out of solution, or a molecular compound, usually water.
17SolubilitySolubility – ability to dissolveIn a double replacement (precipitate) reaction, one of the products must be insoluble in water and form a precipitatePrecipitate – insoluble solid formed by a reaction in solutionIf both products are soluble the result is “no reaction”Solubility rules help you determine whether or not a compound will form a precipitate or remain an aqueous solution
19Combustion Reactions CxHx + O2 CO2 + H2O A substance combines with oxygen, releasing a large amount of energy in the form of light and heat.Produces a flameFuel + oxygen produces carbon dioxide and water vaporCxHx + O2 CO2 + H2O
20Acid-Base Neutralization Reactions When the solution of an acid and solution of a base are mixedProducts have no characteristics of either the acid or the baseAcid + Base (metal hydroxide) salt + waterSalt comes from cation of base and anion of acidHY + XOH XY + H2O
21Chemical EquationsMolecular Equation – shows complete chemical formulas of reactants and productsPb(NO3)2(aq) + 2KI(aq) PbI2(s) + 2KNO3(aq)Complete Ionic Equation – All soluble electrolytes shown as ionsPb+2(aq) + 2NO3-(aq) + 2K+(aq) + 2I-(aq) PbI2(s) + 2K+(aq) + 2NO3-(aq)Net Ionic Equation – shows only the ions and molecules directly involved in the equationPb+2(aq) + 2I-(aq) PbI2(s)
22Writing Complete Ionic Equations Start with a balanced molecular equation.Break all soluble strong electrolytes (compounds with (aq) beside them) into their ions.indicate the correct formula and charge of each ionindicate the correct number of each ionwrite (aq) after each ionBring down all compounds with (s), (l), or (g) unchanged.
24Spectator IonsAppear in identical forms among both the reactants and products of a complete ionic equationWhen writing net ionic equations they cancel each other outPb+2(aq) + 2NO3-(aq) + 2K+(aq) + 2I-(aq) PbI2(s) + 2K+(aq) + 2NO3-(aq)
25Writing Net Ionic Equations Cancel out spectator ions from complete ionic equation then write what’s left6Na+(aq) + 2PO43-(aq) + 3Ca2+(aq) + 6Cl-(aq) 6Na+(aq) + 6Cl-(aq) + Ca3(PO4)2(s)Becomes…2PO43-(aq) + 3Ca2+(aq) Ca3(PO4)2(s)
26PracticeWrite complete ionic and net ionic equations for the following:3(NH4)2CO3(aq) + 2Al(NO3)3(aq) 6NH4NO3(aq) + Al2(CO3)3(s)2NaOH(aq) + H2SO4(aq) Na2SO4(aq) + 2H2O(l)Zn(s) + CuSO4(aq) --> ZnSO4(aq) + Cu(s)
28StoichiometryThe study of the quantitative aspects of chemical reactions.
29Mole RatioConversion factor that relates amount in moles of any two substances involved in a chemical reaction2 Al2O3(l) 4 Al(s) + 3 O2(g)Mole ratio Al2O3 to O2 = 2:3Mole ratio Al to Al2O3 = 4:2 or 2:1Mole ratio Al to O2 = 4:3
30Stoichiometry Problems Solved just like conversions!You must start with a balanced chemical equationTypes:Mole MoleMass MassMass Mole or Mole Mass
31Mole Mole 2 Al2O3(l) 4 Al(s) + 3 O2(g) How many moles of O2 are produced from 3.5 moles of Al2O3?3.5 mol Al2O3 × = 5.25 mol O2*Use mole ratio to convert between moles!3 mol O22 mol Al2O3
32Mass Mass 2 Al2O3(l) 4 Al(s) + 3 O2(g) How many grams of Al are produced from 4.56 grams of Al2O3?Molar Mass Al2O3 = g/mol Molar Mass Al = g/mol4.56 g Al2O3 × × × = 2.41 g Al1 mol Al2O3g Al2O34 mol Al2 mol Al2O326.98 g Al1 mol Al
33Limiting/Excess Reactant Recipe makes 10 pancakes3 eggs2 cups bisquik1 cup milk1 cup chocolate chipsWhat is the most amount of pancakes that I can make with 6 eggs and 5 cups of milk?What is the most amount of pancakes that I can make with 3 cups of chocolate chips and 8 cups of milk?What “limits” how many pancakes I can make and what will be left over?
34Limiting/Excess Reactant The limiting reactant is the reactant that is consumed first, limiting the amounts of products formed.The excess reactant is the reactant that is leftover after the reaction has gone to completion.
36Calculating Limiting/Excess Reagent 2 NO(g) + O2 (g) NO2(g)Given 12.4 grams of NO and 9.40 grams of O2, which is the limiting and which is the excess reagent?1 mol NO30.01 g NO2 mol NO22 mol NO46.01 g NO21 mol NO212.4 g NO × × × = g NO21 mol O216.00 g O22 mol NO21 mol O246.01 g NO21 mol NO29.40 g O2 × × × = g NO2
37Calculating Limiting/Excess Reagent 2 NO(g) + O2 (g) NO2(g)1 mol NO30.01 g NO2 mol NO22 mol NO46.01 g NO21 mol NO212.4 g NO × × × = g NO21 mol O232.00 g O22 mol NO21 mol O246.01 g NO21 mol NO29.40 g O2 × × × = g NO2NO limits the amount of NO2 that is madeLimiting reagent = NOO2 will be leftover once the reaction is completeExcess reactant = O2
38Calculating Limiting/Excess Reagent 2 NO(g) + O2 (g) NO2(g)How much O2 will be in excess once the reaction is complete?1 mol NO30.01 g NO1 mol O22 mol NO32.00 g O21 mol O212.4 g NO × × × = 6.61 g O26.61 grams of O2 will be used in the reaction. You have 9.40 grams to start with.9.40 – 6.61 = 2.79 grams O2 in excess (leftover)
39Limiting/Excess Reactant If the equation has 2 or more products, when determining the limiting/excess reactants, simply pick one of the products and convert both reactants to that product.You MUST use the same product for both.
40Percent Yield Actual Yield × 100 Theoretical Yield Percentage comparing how much product was actually produced compared to what should have been produced.Calculate theoretical yield using stoichiometry.If you know how much of each reactant you start out with, use stoichiometry to calculate how much of the given product you should produce.
41AgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq) Percent YieldAgNO3(aq) + KCl(aq) → AgCl(s) + KNO3(aq)An experiment was performed combining using 3.4 g of AgNO3 and an unlimited supply of KCl. If the experiment yielded 2.7 g of AgCl, what is the percent yield of the experiment?1 mol AgNO3g AgNO31 mol AgCl1 mol AgNO3g AgCl1 mol AgCl3.4 g AgNO3 × × × = 2.9 g AgCl2.72.9Percent Yield = × 100 = 93%