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Unit 6 Chemical Reactions General Chemistry Spring 2010
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NOMENCLATURE REVIEW Section 1
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Ionic Basic Rules ◦ These have a cation (+) and an anion (-) ◦ Usually a metal and a nonmetal ◦ Sometimes contain polyatomic ion(s) (back of PT) ◦ Pay attention to charges Overall charge on ENTIRE formula has to be ZERO Use subscripts to add charge to make zero Criss-cross is a shortcut but be careful! ◦ Practice this on the next slide
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Basic Ionic Formula Give the formulas for the following compounds w/o PAI ◦ Potassium sulfide ◦ Magnesium oxide Give the formulas w/ PAI ◦ (DON’T CHANGE THE FORMULA) ◦ Aluminum nitrate ◦ Calcium phosphate
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Transition Metals In the name, charge on TM is in () ◦ Ex) Iron (III) chloride ◦ Ex) Tin (II) fluoride Use that charge to do criss-cross To figure out the TM charge do reverse criss- cross. The charge is on ONE TM! ◦ Ex) CuO ◦ Ex) Cu 2 O
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Covalent Nomenclature NO CRISS CROSS!!! NO REDUCE!!! The subscript after the symbol = the prefix in the name The prefix in the name = the subscript in the formula (what are these rules?) 1.Ex) NO 2 2.Ex) N 2 O 3.Ex) Sulfur hexafluoride 4.Ex) Triphosphorus pentachloride Diatomic molecules
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Acids Every acid formula begins with hydrogen The other half is either a halogen or a polyatomic ion ◦ Halogen? Use “hydro” in name Ex) HCl Ex) HF ◦ Polyatomic? Change ending to “-ic” (for this class) Ex) H 3 PO 4 Ex) H 2 SO 4 # of H’s is the charge on the PAI
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Section 2 Counting Atoms Review
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Subscript Indicates the number present Only applies to the element it’s with AlCl 3 ◦ One aluminum and three chlorines
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Subscripts When an element has no subscript ◦ The implied subscript is ONE ◦ Ag 1 = Ag
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Coefficient Affects anything behind it Multiply everything by the coefficient 3 AlCl 3 ◦ Three aluminums and nine chlorines
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Section 3 Reaction Basics
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Chemical Equations The “sentences” of chemistry Show how elements react with each other and what compounds they will form So that’s what happens when sodium and water mix!!!!
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Parts of a chemical Equation Reactants ◦ Always on the left of the equation ◦ What the reaction STARTS with Products ◦ Always on the right of the equation ◦ What is produced from the reaction (made) Yield ◦ Arrow ◦ Where the reaction actually occurs
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Can you show me what you just said??? Mg + O 2 MgO ReactantsProducts Yield Sign
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Symbols in Equations (Table 11.1) SymbolExplanation +Used to separate 2 reactions or 2 products “Yields,” separates reactions from products Used in place of for reversible rxns (s)Designates a R or P in the solid state; placed after the formula (l)A R or P in the liquid state; placed after formula (g)“ ” in the gas state; “ ” (aq)Designates an aqueous solution; the substance is dissolved in water; placed after formula heat Indicates that head is supplied to the rxn Pt A formula written above the yield sign indicates its use as a catalyst (in this example, platinum)
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Section 4 Inventory Reactions
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Law of Conservation of Mass The reason we balance reactions Matter is neither created nor destroyed ◦ Must account for all elements Before and after reaction Antoine-Laurent de Lavoisier was the first to state this law.
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Reaction Anatomy KClO 3 KCl + O 2 K1 Cl1 O3 K1 Cl1 O2 Reactant(s)Products
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Inventory Compare the number of each atom in the reactants to the products ◦ If equal = “balanced reaction” Abides by the law of conservation of mass ◦ If not equal = “not balanced” Does not abide by the law of conservation of mass; MUST BALANCE KClO 3 KCl + O 2 K1 Cl1 O3 K1 Cl1 O2 “Not balanced” Reactant(s)Products
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Section 5 Balancing Reactions
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Balance 1. Inventory first 2. Locate one element that does not balance 3. Add a coefficient to make it balance ◦ NEVER TOUCH A SUBSCRIPT ◦ Look to make odd numbers even 4. Re inventory 5. Repeat until balanced KClO 3 KCl + O 2 K1 Cl1 O3 K1 Cl1 O2 2 2 2 6 32 2 2 6 balanced It’s best to leave H and O for the end
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Balancing When balancing a chemical equation you may only change the coefficient (big number in front of the substance) Balancing example #1: ◦ Mg (s) + O 2 (g) MgO (s) 1Mg 1 2 O 1 22 2 / / 2
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Balance Combustion = 2 CHOR Combustion is any reaction with CO 2 + H 2 O for products 2…coefficient of 2 in front of big hydrocarbon C…balance carbons H…balance hydrogen O…balance oxygen R…reduce if possible (divide by a common factor, like 2) C 7 H 16 + O 2 CO 2 + H 2 O2141622 11178 H C
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Balancing (cont.) When balancing a chemical equation you may only change the coefficient (big number in front of the substance) Balancing example #3: ◦ NaOH(aq) + H 2 SO 4 (aq) Na 2 SO 4 (aq) + HOH(l) 1Na 2 1 OH 1 2 H 1 1 SO 4 1 22 / 2 2 / Count polyatomic ions as one piece!
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Practice Problem #1 Balance the following reactions: ◦ P 4 (s) + O 2 (aq) P 4 O 10 ◦ Zn + HCl ZnCl 2 + H 2 (g) ◦ Mg (s) + O 2 (g) MgO (s) ◦ KClO 3 KCl + O 2 (g) 5 2 2 2 223
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Section 6 Reaction Types
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Chemical reactions are classified into 5 different types: ◦ This makes it easier to see what is happening in a reaction ◦ This makes it easier to predict products in a reaction Sorting into piles makes it easier to see the similarities and differences
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Reaction Types (cont.) Five reaction types ◦ 1) Synthesis (Combination) ◦ 2) Decomposition ◦ 3) Single Replacement ◦ 4) Double Replacement ◦ 5) Combustion Now let’s look at each type individually
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Please Note The following reactions are not balanced The examples are only used to show the type of reaction
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Synthesis = S (Note: The book uses the term “combination;” it’s the same thing) Two or more substances react to form one new compound Element + element new compound compound + compound new compound Examples ◦ H 2 + N 2 NH 3 ◦ Mg + O 2 MgO (magnesium oxide)
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Decomposition = D One compound breaks into two or more simpler products Compound element/compound + element/compound Examples ◦ Na 2 O Na + O 2 ◦ NH 4 NO 3 N 2 O + H 2 O Ammonium nitrate, when heated, explosively breaks down!
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Single Replacement = SR Element + compound new element + new compound Examples ◦ AlCl 3 + O 2 Al 2 O 3 + Cl 2 ◦ H 2 (SO 4 ) + K K 2 (SO 4 ) + H 2 ◦ Br 2 + NaI NaBr + I 2 ◦ Br 2 + NaCl No Reaction Halogen activity decreases as you go down group
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Activity Series Whether one metal displaces another depends on upon the reactivities of the metals A reactive metal will replace any metal listed below it on the activity series ◦ Ex) iron will displace copper from a copper compound, but iron does not similarly displace zinc or calcium NameSymbol Decreasing activity LithiumLi PotassiumK CalciumCa SodiumNa MagnesiumMg AluminumAl ZincZn IronFe LeadPb (Hydrogen)(H)* CopperCu MercuryHg SilverAg * Metals from Li to Na will replace H from acids and water; from Mg to Pb they will replace H from acids only
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Double Replacement = DR Compound + compound new compound + new compound Examples ◦ Na 2 O + MgBr 2 NaBr + MgO ◦ H(NO 3 ) + Mg(OH) 2 H(OH) + Mg(NO 3 ) 2 Which switch? Think about Paula Abdul when you rewrite the formulas!
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Combustion = C An element or a compound reacts with oxygen, usually producing heat and light Always involves oxygen as a reactant Reaction with CO 2 + H 2 O for products Examples ◦ C 6 H 12 O 6 + O 2 CO 2 + H 2 O ◦ 2 C 8 H 18 + 25 O 2 16 CO 2 + 18 H 2 O
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Visual Review of Types of Reactions Single Replacement Double Replacement Combustion Decomposition Synthesis
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Section 7 Predicting Products (p.338-339)
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Synthesis (cont.) Steps to predict products: ◦ 1. Combine the two reactants in one product (switchy switchy ◦ 2. Balance Steps in the Irish Countryside
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Practice Problem #4 Predict the product and balance: ◦ Mg (s) + O 2 (g) ◦ Be (s) + Br 2 (g) ◦ Cs (s) + S 2 (g) MgO (s) BeBr 2 (s) Cs 2 S (s) 2 2 4 2
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Decomposition (cont.) Steps to predict products: ◦ 1. Break the one reactant into two products Don’t forget about diatomic molecules H, N, O, F, Cl, Br, I ◦ 2. Balance Ancient Steps in Cancun, Mexico
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Practice Problem #5 Predict the products and balance: ◦ MgCl 2 (s) ◦ FeS (s) ◦ NaI (s) Mg (s) + Cl 2 (g) Fe (s) + S (s) Na (s) + I 2 (s) 2 2
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Single Replacement (cont.) Steps to predict products: ◦ 1. Figure out which metal is going to replace which other metal ◦ 2. Write the products: One metal is now by itself One metal is now part of a compound (Switchy Switchy) ◦ 3. Balance Steps to the House of the Ñusta at Machu Picchu
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Practice Problem #2 Predict the products and balance: ◦ K (s) + MgS (aq) ◦ Ba (s) + Au(C 2 H 3 O 2 ) 3 (aq) ◦ Zn (s) + HCl (aq) Mg (s) + K 2 S (aq) Au (s) + Ba(C 2 H 3 O 2 ) 2 (aq) H 2 (s) + ZnCl 2 (aq) 2 3 322 2
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Double Replacement (cont.) Steps to predict products: ◦ 1. Figure out which metal is going to trade partners with which other metal ◦ 2. Write the products: One metal is now in a compound with the other anion (switchy switchy) ◦ 3. Balance Steps on a Sand Dune at the edge of the Gobi Desert
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Practice Problem #3 Predict the products and balance: ◦ FeS (s) + HCl (aq) ◦ CaCl 2 (aq) + H 2 SO 4 (aq) ◦ NH 4 I (aq) + AgNO 3 (aq) FeCl 2 (aq) + H 2 S (g) HCl (aq) + CaSO 4 (s) NH 4 NO 3 (aq) + AgI (s) 2 2
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Combustion (cont.) Steps to predict products: ◦ 1. Write CO 2 and H 2 O as the products ◦ 2. Balance…2CHOR 1 st balance C 2 nd balance H 3 rd balance O Steps to the Lincoln Memorial
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Practice Problem #6 Predict the products and balance: ◦ C 3 H 8 (g) + O 2 (g) ◦ C 5 H 12 O (s) + O 2 (g) ◦ C 4 H 10 (s) + O 2 (g) CO 2 (g) + H 2 O (l) 534 2151012 2 13 8 10
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Section 8 Reaction Rates and Equilibrium
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Energy Basics For a reaction to proceed… ◦ Reactants’ bonds must break ◦ Bonds must reform to make products Energy is required to break reactants apart (their bonds) Reactions either gain or lose energy, they never stay the same
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Activation Energy Bonds must break in order to reform Energy required to break bonds = ACTIVATION ENERGY All reactions require this The activation energy is always positive
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Energy Diagram Reactants Products NaBr + Li(OH) LiBr + Na(OH) Energy in Kilojoules (kJ) Time Energy of reactants Energy of products
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Energy Diagram Reactants Products NaBr + Li(OH) LiBr + Na(OH) Energy in Kilojoules (kJ) Time Reactants Products The difference between the energy of reactants and products = The total heat or energy of the reaction OR ΔH (change in heat)
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Activation Energy Reactants Products (bonds have reformed) NaBr + Li(OH) LiBr + Na(OH) Na +1 Li +1 Br -1 (OH) -1 Bonds are broken Takes Energy The energy required to break the reactants’ bonds = ACTIVATION ENERGY Reactants Products NaBr + Li(OH) LiBr + Na(OH)
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Activated Complex Energy in Kilojoules (kJ) Time Na +1 Li +1 Br -1 (OH) -1 Bonds are broken Reactants Products NaBr + Li(OH) LiBr + Na(OH) Reactants Products The point at which all bonds have been broken and products begin to reform = ACTIVATED COMPLEX
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Summary Energy in Kilojoules (kJ) Time Reactants Products NaBr + Li(OH) LiBr + Na(OH) Reactants Products Activated Complex Activation Energy Total heat of reaction or ΔH
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Rates of Reaction Ways to make reactions happen faster: ◦ Make chemicals at higher concentration ◦ Increase the temperature ◦ Make the particles smaller ◦ Add a catalyst
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Rates of Reactions (cont.) Catalysts lower the activation energy
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Heats of Reaction Reactions can either… ◦ Give off heat Exothermic The energy level at the end of the reaction is lower than the energy level at the beginning of the reaction Therefore, the change in heat (∆H) is negative ◦ Take in heat Endothermic The energy level at the end of the reaction is higher than the energy level at the beginning of the reaction Therefore, the change in heat (∆H) is positive Feels Hot Feels Cold
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Exothermic Reaction ◦ Reaction loses heat ◦ Δ H value is always negative Endothermic Reaction ◦ Reaction gains heat ◦ Δ H value is always positive energy time energy time Exo vs Endothermic Reactions
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Bond Formation (cont.) Example #1 ◦ Endo or exothermic? ◦ Energy of the Activated complex? ◦ ∆H? Reactants (500 kJ) Products (200 kJ) Act. Energy (150 kJ) Exothermic 650 kJ -300 kJ
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Bond Formation (cont.) Example #2 ◦ Endo or exothermic? ◦ Activation energy? ◦ Energy of products? Endothermic 750 kJ 600 kJ Reactants (200 kJ) ∆H (400 kJ) Activated Complex (950 kJ)
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