cm9 - Chapter 11 Chemical Reactions 1 All chemical...

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Unformatted text preview: Chapter 11 Chemical Reactions 1 All chemical reactions have two parts q Reactants - the substances you start with q Products- the substances you end up with q The reactants turn into the products. q Reactants → Products q 2 In a chemical reaction The way atoms are joined is changed q Atoms aren’t created or destroyed. q Can be described several ways q In a sentence – Copper reacts with chlorine to form copper (II) chloride. q In a word equation q Copper + chlorine → copper (II) chloride q 3 Symbols used in equations Table 11.1 q the arrow separates the reactants from the products q Read “reacts to form” q The plus sign = “and” q (s) after the formula -solid q (g) after the formula -gas q (l) after the formula -liquid q 4 Symbols used in equations (aq) after the formula - dissolved in water, an aqueous solution. q ↑ used after a product indicates a gas (same as (g)) q ↓ used after a product indicates a solid (same as (s)) q 5 Symbols used in equations indicates a reversible reaction (More later) ∆ heat q → , → shows that heat is supplied to the reaction Pt q → is used to indicate a catalyst used in this case, platinum. q 6 What is a catalyst? A substance that speeds up a reaction without being changed by the reaction. q Enzymes are biological or protein catalysts. q 7 Skeleton Equation Uses formulas and symbols to describe a reaction q doesn’t indicate how many. q All chemical equations are sentences that describe reactions. q 8 Convert these to equations q Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form solid iron (II) chloride and hydrogen sulfide gas. 9 Convert these to equations q Nitric acid dissolved in water reacts with solid sodium carbonate to form liquid water and carbon dioxide gas and sodium nitrate dissolved in water. 10 The other way q Fe(g) + O2(g) → Fe2O3(s) 11 The other way q Cu(s) + AgNO3(aq) → Ag(s) + Cu(NO3)2(aq) 12 Balancing Chemical Equations 13 Balanced Equation Atoms can’t be created or destroyed q All the atoms we start with we must end up with q A balanced equation has the same number of atoms of each element on both sides of the equation. q 14 C q q + O O → O C O C + O2 → CO 2 This equation is already balanced q What if it isn’t already? 15 C + O O → C O q q C + O2 → CO We need one more oxygen in the products. q Can’t change the formula, because it describes what actually happens 16 C + O O → C O Must be used to make another CO q But where did the other C come from? q Must have started with two C q 2 C + O2 → 2 CO q 17 1 Write the correct formulas for all the reactants and products 2 Count the number of atoms of each type appearing on both sides 3 Balance the elements one at a time by adding coefficients (the numbers in front) 4 Check to make sure it is balanced. 18 Rules for balancing Never q Change a subscript to balance an equation. – If you change the formula you are describing a different reaction. – H2O is a different compound than H2O2 q 19 Never put a coefficient in the middle of a formula – 2 NaCl is okay, Na2Cl is not. Example 2O 2 H + O → H H O 2 2 22 R P 42H 24 2O 12 Recount Changes the O Also changes the H Make a table to keep track of where you Need twice as much H in the reactant Need twice as much O in the product The equation is balanced, has the same number of each kind of atom on both sides are at 20 Example 2 H + O → 2 2 2HO 2 R P 42H 24 2O 12 This is the answer Not this 21 Examples CH4 + O2 → CO2 + H2O 22 Examples AgNO3 + Cu → Cu(NO3)2 + Ag 23 Examples Al + N2 → Al2N3 24 Examples P+ O2 → P4O10 25 Examples Na + H2O → H2 + NaOH 26 Techniques If an atom appears more than once on a side, balance it last. q If you fix everything except one element, and it is even on one side and odd on the other, double the first number, then move on from there. q C4H10 + O2 CO2 + H2O q 27 27 Types of Reactions Predicting the Products 28 Types of Reactions There are too many reactions to remember q Fall into categories. q We will learn 5 types. q Will be able to predict the products. q For some we will be able to predict whether they will happen at all. q Must recognize them by the reactants q 29 #1 Combination Reactions Combine - put together q 2 elements, or compounds combine to make 1 compound. q q q q Ca +O2 → CaO SO3 + H2O → H2SO4 30 We can predict the products if they are two elements. q M g + N2 → Write and balance q Ca + Cl2 → 31 Write and balance q Fe + O2 → iron (II) oxide 32 Write and balance q Al + O2 → q Remember that the first step is to write the formula Then balance q Also called synthesis reaction q 33 Combining two compounds If they tell you it is combination, you will make one product q Two compounds will make a polyatomic ion. q CO2 + H2O → q q H2O + Cl2O7→ 34 34 #2 Decomposition Reactions q q decompose = fall apart one reactant falls apart into two or more elements or compounds. electricity NaCl → Na + Cl2 ∆ → q CaCO CaO + CO2 3 q 35 #2 Decomposition Reactions Can predict the products if it is a binary compound q Made up of only two elements q Falls apart into its elements electricity q H O → q 2 36 #2 Decomposition Reactions q HgO → ∆ 37 #2 Decomposition Reactions If the compound has more than two elements you must be given one of the products q The other product will be from the missing pieces ∆ q NiCO → NiO + q 3 q 38 H2CO3(aq)→ CO2 + #3 Single Replacement One element replaces another q Reactants must be an element and a compound. q Products will be a different element and a different compound. q Na + KCl → K + NaCl q q F2 + LiCl → LiF + Cl2 39 Na + KCl → K + NaCl Na K Cl 40 40 F2 + 2 LiCl → 2 LiF + Cl2 F F Li Cl Li Cl 41 41 #3 Single Replacement Metals replace metals (and hydrogen) q Al + CuSO4 → q q q Zn + H2SO4 → Think of water as HOH q Metals replace one of the H, combine with hydroxide. q Na + HOH → 42 #3 Single Replacement We can tell whether a reaction will happen q Some are more active than other q More active replaces less active q There is a list on page 333 q 43 #3 Single Replacement There is a list on page 333 q Higher on the list replaces lower. q If the element by itself is higher, it happens, q if element by itself is lower, it doesn’t q 44 q q Note the * #3 Single Replacement H can be replaced in acids by everything higher q Only the first 4 (Li - Na) react with water. 45 q Al + HCl → #3 Single Replacement 46 q Fe + CuSO4 → #3 Single Replacement 47 q Pb + KCl → #3 Single Replacement 48 q Al + H2O → #3 Single Replacement 49 #3 Single Replacement q What does it mean that Ag is on the bottom of the list? 50 #3 Single Replacement q Nonmetals can replace other nonmetals Limited to F2 , Cl2 , Br2 , I2 q q The order of activity is that on the table. q Higher replaces lower. q F2 + HCl → q 51 Br2 + KCl → #4 Double Replacement Two things replace each other. q Reactants must be two ionic compounds or acids. q Usually in aqueous solution q NaOH + FeCl3 → q The positive ions change place. q q 52 q NaOH + FeCl3 → NaOH + FeCl3 → Fe3+OH- + Na+ClFe(OH)3 + NaCl 3NaOH + FeCl3 → Fe(OH)3 + 3NaCl Na+ OH+ ClNa+ OH+ ClFe3+ ClNa+ OH+ 53 53 #4 Double Replacement Will only happen if one of the products – doesn’t dissolve in water and forms a solid – or is a gas that bubbles out. – or is a covalent compound usually water. q Polyatomic ions don’t change from side to side q 54 Complete and balance q assume all of the reactions take place. CaCl2 + NaOH → CuCl2 + K2S → KOH + Fe(NO3)3 → q q q 55 Complete and balance q KOH + Fe(NO3)3 → q H3PO4 + Ca(OH)2 → 56 56 How to recognize which type Look at the reactants q E for element q C for compound qE+E Combination qC Decomposition qE+C Single replacement q C + C Double replacement q 57 Last Type Combustion q A compound composed of only C H and maybe O is reacted with oxygen q If the combustion is complete, the products will be CO2 and H2O. q q If the combustion is incomplete, the products will be CO and H2O. 58 or just C and H2O. q O2 will always be the second reactant q Examples q Complete combustion of C4H10 q Incomplete combustion of C4H10 59 Examples q Complete combustion of C6H12O6 q Incomplete combustion of C2H6O 60 Ionic Compounds and acids Fall apart into ions when they dissolve q That’s why they conduct electricity when dissolved. q So when we write them as (aq) they are really separated q NaCl(aq) is really Na+(aq) and Cl-(aq) q K2SO4 (aq) is really K+(aq) and SO42-(aq) q 61 61 Reactions in aqueous solutions Many reactions happen in solution q Makes it so the ions separate so they can interact. q Solids, liquids, and gases are not separated, only aqueous q 62 62 Every aqueous compound is written as separate ions q Solids, liquids and gases as whole compounds q MgCl2(aq) + PbSO4(aq) → MgSO4(aq) + PbCl2(s) q Complete Ionic Equation 63 Is really q Mg2+(aq) + Cl-(aq) + Pb2+(aq) + SO4(aq) → Mg2+(aq) + SO4(aq) + PbCl2(s) q 63 Write the complete ionic equation for q 3+ + FeBr-3(aq) + KOH(aq) → FeBr (aq) KOH-(aq) (aq) (aq) + KBr (aq) (aq) KBr-(aq) + Fe(OH)3(s) 3 + + + + + → 64 64 Write the complete ionic equation for q CaCl2(aq) + MgSO4(aq) → CaSO4(s) + MgCl2(aq) 65 65 Write the complete ionic equation for q Ba(OH)2(aq) + H2SO4(aq) → BaSO4(s) + HOH(l) 66 66 The complete ionic equation is q Fe3+(aq)+ Br-(aq) + K+(aq) +OH-(aq) → K+(aq) +Br-(aq) + Fe(OH)3(s) K+ and Br- don’t change. q They are spectator ions q Could be eliminated q Fe3+(aq) +OH-(aq) →Fe(OH)3(s) q q 67 This is what really changes 67 Net ionic equation Shows only those particles that change before and after. q Eliminate spectator ions q Needs to be balanced in terms of both mass and charge q Fe3+(aq) +OH-(aq) →Fe(OH)3(s) q q Fe3+(aq) +3 OH-(aq) →Fe(OH)3(s) 68 68 Write the net ionic equation q HCl (aq) + Ba(OH)2 (aq) → BaCl2(s) + HOH (l) 69 69 Write the net ionic equation q Al + FeSO4(aq) → Al2(SO4)3(aq) + Fe 70 70 Write the net ionic equation q Cl2(s) + NaI(aq) → NaCl(aq) + I2(s) 71 71 Write the net ionic equation q K2CO3(aq) + MgI2(aq) → MgCO3(s) + KI(aq) 72 72 Net ionic equations q Written for single and double replacement. 73 73 Predicting precipitates Solids formed from aqueous solution. q You can predict them if you know some general rules for solubility. q 74 74 These things are soluble 1. 2. 3. Salts with alkali metals and ammonium Salts of nitrates and chlorates Salts of sulfates except Ag+, Pb2+, Hg22+, Ba2+, and Sr2+ Salts of chlorides except Ag+, Pb2+, and Hg22+ 4. 75 75 These things are insoluble 1. q Carbonates, phosphates, chromates, sulfides, and hydroxides Unless they fall under rule # 1 76 76 Is it soluble? LiBr q Ba(NO3)2 q q q q q q 77 CaSO4 PbCl2 CaCO3 K2CO3 Cd(ClO3)2 77 Is there a reaction? For double replacement- has to make gas, solid or water. q Water from an acid- H+ and a hydroxide- OH- makes HOH q Solids- from solubility rules q Exchange ions and see if something is insoluble q 78 78 Is there a reaction? q MgSO4 + NaOH → H2SO4 + KOH → K3PO4 + FeF3→ q q 79 79 Chapter 7 Summary 80 An equation Describes a reaction q Must be balanced to follow the Law of Conservation of Mass q Can only be balanced by changing the coefficients. q Has special symbols to indicate state, and if catalyst or energy is required. q 81 Reactions Come in 5 types. q Can tell what type they are by the reactants. q Single Replacement happens based on the activity series q Double Replacement happens if the product is a solid, water, or a gas. q 82 The Process 1. Determine the type by looking at the reactants. 2. Put the pieces next to each other based on type 3. Use charges to write the formulas – Elements get 2? 4. Use coefficients to balance the equation. 83 ...
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cm9 - Chapter 11 Chemical Reactions 1 All chemical...

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