Presentation on theme: "Unit 5 Chemical Equations & Reactions"— Presentation transcript:
1 Unit 5 Chemical Equations & Reactions Honors Chemistry
2 All chemical reactions have two parts:Reactants - the substances you start withProducts- the substances you end up withThe reactants turn into the products.Reactants ® Products
3 In a chemical reaction The way atoms are joined is changed Atoms aren’t created of destroyed.Can be described several ways:1. In a sentenceCopper reacts with chlorine to form copper (II) chloride.2. In a word equationCopper + chlorine ® copper (II) chloride
4 Symbols in equationsthe arrow separates the reactants from the productsRead “reacts to form”The plus sign = “and”(s) after the formula = solid(g) after the formula = gas(l) after the formula = liquid
5 Symbols used in equations (aq) after the formula - dissolved in water, an aqueous solution. used after a product indicates a gas (same as (g))¯ used after a product indicates a solid (same as (s))
6 Symbols used in equations indicates a reversible reactionshows that heat is supplied to the reactionis used to indicate a catalyst is supplied, in this case, platinum.
7 What is a catalyst?A substance that speeds up a reaction, without being changed or used up by the reaction.Enzymes are biological or protein catalysts.
8 Skeleton Equation Uses formulas and symbols to describe a reaction doesn’t indicate how many.All chemical equations are sentences that describe reactions.
9 Convert these to equations Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.
11 Balanced Equation Atoms can’t be created or destroyed All the atoms we start with we must end up withA balanced equation has the same number of each element on both sides of the equation.
12 Rules for balancing:Assemble, write the correct formulas for all the reactants and productsCount the number of atoms of each type appearing on both sidesBalance the elements one at a time by adding coefficients (the numbers in front) - save H and O until LAST!Check to make sure it is balanced.
13 Never Never change a subscript to balance an equation. If you change the formula you are describing a different reaction.H2O is a different compound than H2O2Never put a coefficient in the middle of a formula2 NaCl is okay, Na2Cl is not.
14 ExampleH2 +O2H2ORP2H22O1Need twice as much O in the product
23 Types of Reactions There are millions of reactions. Can’t remember them allFall into several categories.We will learn 5 major types.Will be able to predict the products.For some, we will be able to predict whether they will happen at all.Will recognize them by the reactants
24 CaO(s) + SO2(g) CaSO3(s) COMBINATION REACTIONA reaction in which two or more substances combine to form a single product.A +B + C ABCCaO(s) + SO2(g) CaSO3(s)
25 Write and balance Ca + Cl2 ® Fe + O2 ® Al + O2 ® Remember that the first step is to write the correct formulasThen balance by using coefficients only
26 DECOMPOSITION REACTION A reaction in which a single compound reacts to give two or more substances, usually requiring a raise in temperature.ABC A + B + C2KClO3(s) 2KCl(s) + 3O2(g)
27 #2 - Decomposition Reactions decompose = fall apartone reactant falls apart into two or more elements or compounds.NaCl Na + Cl2CaCO CaO + CO2Note that energy is usually required to decompose
28 #2 - Decomposition Reactions Can predict the products if it is a binary compoundMade up of only two elementsFalls apart into its elementsH2OHgO
29 Can predict the products if it is a binary compound 2H2O(l) →Can predict the products if it is a binary compoundMade up of only two elementsFalls apart into its elementsFig. 8-13, p. 215
30 #2 - Decomposition Reactions If the compound has more than two elements you must be familiar with page 10 of your packetNiCO3 ®KClO3(aq) ®
31 Single Displacement (or Replacement) Reactions pp. 218, 220
33 Single Displacement (or Replacement) Reactions PREDICT THE PRODUCT1. Ca + HCl 2. ZnBr2 + I2 3. Cu + AgNO3 Answers are on the next slide.
34 #3 Single Replacement Metals replace other metals (and hydrogen) K + AlN ®Zn + HCl ®Think of water as HOHMetals replace one of the H, combine with hydroxide.Na + HOH ®
35 We can tell whether a reaction will happen Some chemicals are more “active” than othersMore active replaces less activeThere is a list on page 11 - called the Activity Series of MetalsHigher on the list replaces lower.
36 #3 Single Replacement Note the * concerning Hydrogen H can be replaced in acids by everything higherLi, K, Ba, Ca, & Na replace H from acids and waterFe + CuSO4 ®Pb + KCl ®Al + HCl ®
37 #3 - Single ReplacementWhat does it mean that Hg and Ag are on the bottom of the list?Nonmetals can replace other nonmetalsLimited to F2 , Cl2 , Br2 , I2 (halogens)Higher replaces lower.F2 + HCl ®Br2 + KCl ®
38 Double Displacement (or Replacement) Reactions pp. 220, 223
39 Double Displacement (or Replacement) Reactions PREDICT THE PRODUCT & BALANCE1. MgSO4 + LiOH ___________2. Pb(NO3)2 + Na2CO3 ____________3. HNO3 + Ba(OH)2 ___________Answers are on the next slide.
41 Double Replacement Two things replace each other. Reactants must be two ionic compounds or acids.Usually in aqueous solutionNaOH + FeCl3 ®The positive ions change place.NaOH + FeCl3 ® Fe+3 OH- + Na+1 Cl-1NaOH + FeCl3 ® Fe(OH)3 + NaCl
42 Double Replacement Has certain “driving forces” Will only happen if one of the products:doesn’t dissolve in water and forms a solid (a “precipitate”), oris a gas that bubbles out, oris a covalent compound (usually water).
43 Oxidation and Reduction Reactions Early chemists saw oxidation as the combination of a material with oxygenToday, many of these reactions may not even involve oxygenRedox currently says that electrons are transferred between reactantsAlways occur simultaneously.Called redox reactions.
44 Oxidation and Reduction Reactions Oxidation – refers to a loss of electrons, or gain of oxygenReduction – refers to a gain of electrons, or loss of oxygenOxidizing agent – the substance being reducedReducing agent – the substance being oxidized
45 Oxidation and Reduction Reactions Loss of Electrons is OxidationGain of Electrons is ReductionLEO SAYS GER
46 Rules For Assigning Oxidation States Oxidation numbers are used to keep track of how many electrons are lost or gained by each atom
47 Balancing Redox Reactions If the oxidation number changes, that element has undergone oxidation or reductionReaction as a whole must be redoxHalf-reaction – equation showing just the oxidation or just the reduction
48 Balancing Redox Reactions (in an acid) SO2 + MnO4- →SO42- + Mn2+Divide the equation into half-reactions.SO2 → SO MnO4- → Mn2+Oxidation ReductionBalance all atoms except O and H
49 Balancing Redox Equations Balance O by adding H2O.2H2O + SO2 →SO MnO4- →Mn2+ + 4H2OBalance H by adding H+.2H2O + SO2 → SO H+8H+ + MnO4- → Mn2+ + 4H2O
51 Cancel anything that's the same on both sides. 2H2O + 5SO2 +2MnO4- →2Mn2+ + 5SO H+
52 Balancing Redox Reactions (in a base) Follow steps 1 – 7 then: 8. Identify the number of proton (H+) in the acidic answer. Add the same number of OH+ ions to BOTH sides of the equation. 9. If H+ and OH+ appear on the same side of the equation, they will react in a 1:1 ratio to form H2O. 10. Cancel out water molecules that appear on both sides of the equation. 11. Check that all is balanced
53 PRECIPITATION REACTION A reaction where an insoluble solid is formed during a reaction between two aqueous solutions.(aq) (aq) (aq) (s)2KI(aq) + Pb(NO3)2(aq) 2KNO3(aq) + PbI2(s)Exchange cations
54 Ionic EquationsMany reactions occur in water- that is, in aqueous solutionMany ionic compounds “dissociate”, or separate, into cations and anions when dissolved in waterAgNO3 + NaCl AgCl + NaNO31. this is the full equation2. Write it as an ionic equation3. Eliminating ions not directly involved (spectator ions) = net ionic equation
57 NEUTRALIZATION REACTION A reaction between an acid and a base which results in the production of a salt and water.HA + BOH (metal/nonmetal) + H2OHNO3(aq) + KOH(aq) KNO3(aq) + H2O(l)
58 2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g) COMBUSTION REACTIONMeans “add oxygen”A compound composed of only C, H, and maybe O is reacted with oxygenIf the combustion is complete, the products will be CO2 and H2O.If the combustion is incomplete, the products will be CO (possibly just C) and H2O.A reaction of a substance with oxygen, usually the rapid release of heat produces a flame.CH + O2 CO2 + H2O2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g)
59 2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g) + heat (in Joules) CombustionMany times in a combustion reaction, heat energy is given off. In chemical terms this is called an exothermic reaction.Thermochemistry is field of chemistry which studies the transfer of heat in a reaction.The thermodynamic equation representing this exothermic reaction is:2C4H10(g) + 13O2(g) 8CO2(g) + 10H2O(g) + heat (in Joules)
61 GAS FORMATION REACTIONS A reaction that produces a gas from reactants not in the gaseous state.2 HCl (aq) + ZnS (s) ZnCl2 (aq) + H2S (g)Zn (s) + 2 HCl (aq) ZnCl2 (aq) + H2 (g)Many gas formation reactions involve two steps, first the double displacement reaction then the decomposition reaction of an unstable substance.Na2CO3 + 2HCl 2 NaCl + H2CO3H2CO3 CO2 + H2OBesides carbonic acid (H2CO3), sulfurous acid (H2SO3) also decomposes into SO2 and water.
62 COMMON GAS FORMATION REACTIONS YOU SHOULD REMEMBER NH4OH → NH3 (g) + H2O (l)H2CO3 → CO2 (g) + H2O (l)H2SO3 → SO2 (g) + H2O (l)
63 Remember an equation... Describes a reaction Must be balanced in order to follow the Law of Conservation of MassCan only be balanced by changing the coefficients.Has special symbols to indicate physical state, and if a catalyst or energy is required.