5 In a chemical reactionAtoms aren’t created or destroyed (the Law of Conservation of Mass)A reaction can be described several ways:In a sentence every item is a wordCopper reacts with chlorine to form copper (II) chloride.In a word equation some symbols usedCopper + chlorine ® copper (II) chloride
6 In a skeleton equation – symbols and formulas are used, but the equation might not be balanced N2O3(g) + H2O(l) HNO2(aq)In a balanced equation – symbols and formulas are used and there are the same number of atoms of each element on both sides of the equation
7 Symbols in equations? The plus sign means “and” the arrow (→) separates the reactants from the products (arrow points to products)Read as: “reacts to form” or yieldsThe plus sign means “and”(s) after the formula means solid: Fe(s)(g) after the formula means gas: CO2 (g)(l) after the formula means liquid: H2O(l)
8 ↑ used after a product indicates a gas has been produced: H2↑ (aq) after the formula means dissolved in water, an aqueous solution: NaCl (aq) is a salt water solution ↑ used after a product indicates a gas has been produced: H2↑¯ used after a product indicates a solid has been produced: PbI2↓
9 Symbols used in equations (double arrow) indicates a reversible reactionshows that heat is supplied to the reactionmeans a catalyst is supplied (in this case, platinum is the catalyst)
10 Enzymes are biological or protein catalysts in your body. What is a catalyst?A substance that speeds up a reaction, or lowers the temperature when it can happen, but, is not changed or used up by the reaction.Enzymes are biological or protein catalysts in your body.
11 The Skeleton Equation Uses formulas and symbols to describe a reaction but doesn’t indicate how many; this means they are NOT balancedAll chemical equations are a description of the reaction.
12 Write a skeleton equation for: Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.
13 Write a skeleton equation for: Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas.Fe2S3(s) + HCl(g) FeCl3(s) + H2S(g)
14 Write a skeleton equation for: Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.
15 Write a skeleton equation for: Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water.HNO3(aq) + Na2CO3(s) H2O(l) + CO2(g) + NaNO3(aq)
17 Balanced Chemical Equations Atoms can’t be created or destroyed in an ordinary reaction:All the atoms we start with we must end up with (meaning: balanced!)A balanced equation has the same number of each element on both sides of the equation.
18 Rules for balancing:Write the correct formulas for all the reactants and products, using “+” and “→”Count the number of atoms of each type appearing on both sidesBalance the elements one at a time by adding coefficients (the numbers in front) where you need more –save balancing the H and O until LAST!(hint: save O until the very last)Double-Check to make sure it is balanced.
19 NeverNever change a subscript to balance an equation (You can only change coefficients)If you change the subscript (formula) you are describing a different chemical.H2O is a different compound than H2O2Never put a coefficient in the middle of a formula; they must go only in the front2NaCl is okay, but Na2Cl and Na2Cl are not.
21 Practice Balancing Examples 2 AgNO3 + 1 Cu ® 1Cu(NO3)2 + 2 Ag3 Mg + 1N2 ® 1Mg3N24 P + 5 O2 ® 1P4O102 Na + 2 H2O ® 1 H2 + 2 NaOH1 CH4 + 2 O2 ® 1 CO2 + 2 H2O
22 Types of Reactions There are probably millions of reactions. they will fall into several categories.We will learn: the 5 major types.
23 5 Types of Equations Combination reactions R + S RS Decomposition reactionsRS R + SSingle replacementT + RS TS + RDouble Replacement reactionsRS + TU RU + TSCombustion reactions (add oxygen)Complete CO2 + H2OIncomplete CO + H2O
24 1. Combination Reactions Combine = put together2 substances combine to make one compound (also called “Synthesis”)Ca + O2 ® CaOSO3 + H2O ® H2SO4often the reactants are two elements.Mg + N2 ® Mg3N2
25 Formulas and balancing: First write the correct formulas –subscripts can be written at this point, but not later while balancing!Next balance by changing only the coefficients
26 2. Decomposition Reactions decompose = fall apartone reactant breaks apart into two or more elements or compounds.NaCl Na + Cl2CaCO CaO + CO2Energy (heat, sunlight, electricity, etc.) is usually required
27 2. Decomposition Reactions binary compounds break apart into the elements:H2O H2 + O2HgO Hg + O2
28 3. Single Replacement Reactions One element replaces anotherReactants must be an element and a compound.Products will be a different element and a different compound.Na + KCl ® K + NaClF2 + LiCl ® LiF + Cl2(Cations switched)(Anions switched)
29 3. Single Replacement Reactions Metals will replace other metals (and they can also replace hydrogen)K + AlN ® K3N + AlZn + HCl ® ZnCl2 + H2Think of water as: HOHMetals replace the first H, and then combines with the hydroxide (OH).Na + HOH ® NaOH + H2O
30 3. Single Replacement Reactions To predict whether or not a single replacement reaction will happen:Some chemicals are more “active” than othersMore active replaces less activeTable 7.2 on p. 191 –shows the Activity Series of MetalsHigher on the list replaces those lower.
31 The “Activity Series” of Metals LithiumPotassiumCalciumSodiumMagnesiumAluminumZincChromiumIronNickelLeadHydrogenBismuthCopperMercurySilverPlatinumGoldHigher activityMetals can replace other metals, provided they are above the metal they are trying to replace(for example, zinc will replace lead)Metals above hydrogen can replace hydrogen in acids.Metals from sodium upward can replace hydrogen in water.Lower activity
32 The “Activity Series” of Halogens Higher ActivityHalogens can replace otherhalogens in compounds, provided they are above the halogen they are trying to replace.FluorineChlorineBromineIodineLower Activity2NaCl(s) + F2(g) 2NaF(s) + Cl2(g)???MgCl2(s) + Br2(g) No Reaction!???
33 4. Double Replacement Reactions Two things replace each other.Reactants must be two ionic compounds, in aqueous solutionNaOH + FeCl3 ®The positive ions change place.NaOH + FeCl3 ® Fe+3 OH- + Na+1 Cl-1= NaOH + FeCl3 ® Fe(OH)3 + NaCl
34 4. Double Replacement Reactions Have certain “driving forces”, or reasonsWill only happen if one of the products:a) doesn’t dissolve in water and forms a solid (a “precipitate”), orb) is a gas that bubbles out, orc) is a molecular compound (which will usually be water).
35 How do you know which type? Look at the reactants: (E=element, C=compound)E + E = CombinationC = DecompositionE + C = Single replacementC + C = Double replacement
36 5. Combustion Reactions Combustion means “add oxygen” When a compound made of only C and H (and maybe O) reacts with oxygen – commonly called “burning”Complete combustion forms products of CO2 and H2O.Incomplete combustion forms products of CO (or possibly just C) and H2O.
37 Combustion Reaction Examples: C4H10 + O2 ® CO2 + H2O(complete)C4H10 + O2 ® CO + H2O(incomplete)C6H12O6 + O2 ® CO2 + H2O(complete)C8H8 + O2 ® CO + H2O(incomplete)
38 SUMMARY: 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 the physical state, if a catalyst or energy is required, etc.
39 Reactions Come in 5 major types. Identify the type by looking at the reactants.Single Replacement happens based on the Activity SeriesDouble Replacement happens if one product is: 1) a precipitate (an insoluble solid), 2) water (a molecular compound), or 3) a gas.
40 5 Types of Equations Combination reactions R + S RS Decomposition reactionsRS R + SSingle replacementT + RS TS + RDouble Replacement reactionsRS + TU RU + TSCombustion reactions (add oxygen)Complete CO2 + H2OIncomplete CO + H2O