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What is the difference between a chemical and physical reaction? When you watch a reaction occur, what are some hints that it is a chemical reaction? Ch. 8 Chemical Equations and Reactions 8.1 Describing Chemical Reactions Chemical Reactions when a substance changes identity reactants- original products- resulting law of conservation of mass total mass of reactants = total mass of products Chemical Reactions chemical equation represents identities and relative amounts of reactants and products in the chemical reaction uses symbols and formulas Hints of Chemical Rxn heat can also happen with physical changes gas or light bubbles means a gas is being created as product precipitate solid is being created color change Writing Chemical Equations most pure elements diatomic molecules written as elemental symbol molecule containing only 2 atoms some elements normally exist this way H2, O2, N2, F2, Cl2, Br2, I2, At2 other exceptions sulfur: S8 phosphorus: P4 Word Equations uses names instead of formulas helps you to write formula equation Example Description: Solid sodium oxide is added to water at room temperature and forms sodium hydroxide. Word Equation: sodium oxide + water sodium hydroxide Formula Equation: Na2O + H2O NaOH Symbols Used in Equations yields reversible above arrow: or heat MnO2 or Pt 25°C 2 atm heated catalyst specific T requirement specific P requirement after a formula: (s) solid (l) liquid (aq) aqueous: dissolved in water (g) gas Coefficients whole numbers in front of formula distributes to numbers of atoms in formula specifies the relative number of moles and molecules involved in the reaction used to balance the equation Equations cannot tell us: if the reaction will actually occur depends on many factors affecting energy the speed of the reaction depends on chemical kinetics can be very slow, almost unnoticeably how the bonding actually changes formula may not clearly show bonding Write the word equation from the following description: Zinc metal is added to hydrochloric acid to create zinc chloride and hydrogen gas. Ch. 8 Chemical Equations and Reactions 8.1b Balancing Equations and Writing Formula Equations Balancing Equations 1. 2. 3. 4. 5. 6. ONLY add/change coefficientsNEVER subscripts!!! balance one type of atom at a time balance polyatomic ions first balance atoms that appear only once second balance H and O last simplify if you can Check at end! Writing Equations Write Word equations to help you organize reactants and products Be sure to include symbols showing states of each reactant and product Be sure to write the correct formula for each (crossing over for ionic compounds!) Check your balancing of the equation when you are finished Example 1 Description: Zinc metal is added to hydrochloric acid to create zinc chloride and hydrogen gas. Word Equation: zinc + hydrochloric acid zinc chloride + hydrogen Example 1 Formula Equation: Zn (s) + HCl(aq) ZnCl2(aq) + H2(g) Balanced Formula Equation Zn (s) + 2HCl(aq) ZnCl2(aq) + H2(g) Example 2 Solid calcium metal reacts with water to form aqueous calcium hydroxide and hydrogen gas. calcium + water calcium hydroxide + hydrogen Ca(s) + H2O(l) Ca(OH)2(aq) + H2(g) Ca(s) + 2H2O(l) Ca(OH)2(aq) + H2(g) Example 3 solid zinc metal reacts with aqueous copper (II) sulfate to produce solid copper metal and aqueous zinc sulfate zinc + copper (II) sulfate copper + zinc sulfate Zn(s) + CuSO4(aq) Cu(s) + ZnSO4(aq) Zn(s) + CuSO4(aq) Cu(s) + ZnSO4(aq) Example 4 Hydrogen peroxide in an aqueous solution decomposes to produce oxygen and water hydrogen peroxide oxygen + water H2O2(aq) O2(g) + H2O(l) 2H2O2(aq) O2(g) + 2H2O(l) Example 5 Solid copper metal reacts with aqueous silver nitrate to produce solid silver metal and aqueous copper (II) nitrate copper + silver nitrate silver + copper (II) nitrate Cu(s) + AgNO3(aq) Ag(s) + Cu(NO3)2(aq) Cu(s) + 2AgNO3(aq) 2Ag(s) + Cu(NO3)2(aq) Example 6 Carbon dioxide gas is bubbled through water containing solid barium carbonate, creating aqueous barium bicarbonate carbon dioxide + water + barium carbonate barium bicarbonate CO2(g) + H2O(l) + BaCO3(s) Ba(HCO3)2(aq) CO2(g) + H2O(l) + BaCO3(s) Ba(HCO3)2(aq) Example 7 Acetic acid solution is added to a solution of magnesium bicarbonate to create water, carbon dioxide gas, and aqueous magnesium acetate. acetic acid + magnesium bicarbonate water + carbon dioxide + magnesium acetate HCH3COO(aq) + Mg(HCO3)2(aq) H2O(l) + CO2(g) + Mg(CH3COO)2(aq) 2HCH3COO(aq) + Mg(HCO3)2(aq) 2H2O(l) + 2CO2(g) + Mg(CH3COO)2(aq) Write the balanced formula equation for: Lithium metal is added to a solution of aluminum sulfate to make aqueous lithium sulfate and aluminum metal. Ch. 8 Chemical Equations and Reactions 8.2a Types of Chemical Reactions Types of Chemical Reactions 5 basic types discussed here not all reactions fall in these categories you should be able to: categorize a reaction by its reactant(s) predict the product(s) 1. Synthesis also called composition reaction reactants: more than one can be elements or compounds products: only one compound A + X AX where A is the cation and X is anion 1. Synthesis Rubidium and sulfur Rb(s) + S8(s) Rb2S(s) Magnesium and oxygen Mg(s) + O2(g) MgO(s) Sodium and chlorine Na(s) + Cl2(g) NaCl(s) Magnesium and fluorine Mg(s) + F2(g) MgF2(s) 1. Synthesis calcium oxide and water CaO(s) + H2O(l) Ca(OH)2(aq) sulfur dioxide and water SO2(g) + H2O(l) H2SO3(aq) calcium oxide and sulfur dioxide CaO(s) + SO2(g) CaSO3(s) 2. Decomposition opposite of synthesis usually require energy reactants: only one compound products: more than one usually elements but can be compounds AX A + X 2. Decomposition water H2O(l) H2(g) + O2(g) calcium carbonate CaCO3(s) CaO(s) + CO2(g) calcium hydroxide Ca(OH)2(s) CaO(s) + H2O(l) carbonic acid H2CO3(aq) CO2(g) + H2O(l) 3. Single Replacement an element replaces a similar element in a compound reactants: 1 element & 1 compound products: 1 element & 1 compound A + BX B + AX Y + AX X + AY 3. Single Replacement zinc and hydrochloric acid Zn(s) + HCl(aq) ZnCl2(aq) + H2(g) iron and water Fe(s) + H2O(l) FeO(aq) magnesium and lead (II) nitrate Mg(s) + Pb(NO3)2(aq) Mg(NO3)3(aq) + Pb(s) chlorine and potassium bromide Cl2(g) + KBr(s) KCl(s) + Br2(g) 4. Double Replacement two similar elements switch places reactants: 2 compounds products: 2 compounds AX + BY BX + AY 4. Double Replacement barium chloride and sodium sulfate BaCl2(aq) + Na2SO4(aq) NaCl(aq) + BaSO4(s) iron sulfide and hydrochloric acid FeS(aq) + HCl(aq) FeCl2(aq) + H2S(g) hydrochloric acid and sodium hydroxide HCl(aq) + NaOH NaCl(aq) + H2O(l) potassium iodide and lead (II) nitrate KI(aq) + Pb(NO3)2 KNO3(aq) + PbI2(s) 5. Combustion combines with oxygen releases energy in form of heat/light reactants: O2 + compound/element compound or element must be made of C and H only H2O and/or CO2 depending on element contained in reactants Ex: CH4 + O2 CO2 + H2O Combustion hydrogen and oxygen H2(g) + O2(g) H2O(g) propane and oxygen C3H8(g) + O2(g) CO2(g) + H2O(g) Practice Classify each of the following reactions one of the five basic types: Na2O + H2O NaOH Zn (s) + 2HCl(aq) ZnCl2(aq) + H2(g) Ca(s) + 2H2O(l) Ca(OH)2(aq) + H2(g) Practice 2H2O2(aq) Cu(s) O2(g) + 2H2O(l) + 2AgNO3(aq) 2Ag(s) +Cu(NO3)2(aq) C2H4(g) ZnO(s) + O2(g) CO2(g) + H2O(g) + C(s) 2Zn(s) + CO2(g) Practice Na2O(s) Ca(s) + 2CO2(g) + H2O(l) NaHCO3(s) + H2O(l) Ca(OH)2 (aq) + H2(g) KClO3(s) KCl(s) + O2(g) H2SO4(aq) + BaCl2(aq) HCl(aq) + BaSO4(s) Write the balanced formula equation for the following reaction Identify the type of reaction Aqueous lead (II) nitrate was mixed with a hydrochloric acid to create lead (II) chloride and nitric acid. Ch. 8 Chemical Equations and Reactions 8.2b Predicting Products of Chemical Reactions Types of Reactions we are going to learn how to predict products in simple reactions of each type will need to identify type for more complex reactions but not predict products 1. Synthesis making binary compounds find ions created by each reactant crossover to make product barium metal is reacted with solid sulfur. Ba(s) + S8(s) BaS(s) magnesium metal reacts with bromine Mg(s) + Br2(l) MgBr2(s) 2. Decomposition of binary compounds find elements that will be created write them in natural state Solid silver oxide is heated. Ag2O(s) Ag(s) + O2(s) Water undergoes decomposition. H2O(l) H2(g) + O2(g) 3. Single Replacement Identify the “similar” element in the compound that it will replace Find ions created crossover to make new compound zinc metal is added to solution of lead(II) nitrate Zn(s) + Pb(NO3)2(aq) Zn(NO3)2(aq) + Pb(s) sodium iodide is added to chlorine gas NaI(aq) + Cl2(g) NaCl(aq) + I2(s) 4. Double Replacement identify which parts will switch places find ions that will be created crossover to create new compounds silver nitrate and sodium chloride solutions are mixed AgNO3(aq) + NaCl(aq) NaNO3(aq) + AgCl(s) solutions of magnesium fluoride and potassium hydroxide are mixed MgF2(aq) + KOH(aq) Mg(OH)2(aq) + KF(aq) 5. Combustion always makes H2O and/or CO2 choose based on what elements exist in reactants solid carbon reacts with oxygen C(s) + O2(g) CO2 (g) C2H5OH reacts with oxygen in air. C2H5OH + O2(g) CO2(g) + H2O(l) Example Identify the type of reaction, predict the products, and write the balanced chemical equation: Hydrogen sulfide gas is bubbled through a solution of potassium hydroxide Example Liquid butanol (C4H9OH) is burned in oxygen gas. compound + oxygen: C C4H9OH (l) + 6O2(g) 5H2O(l) + 4CO2(l) Liquid bromine is mixed with sodium iodide solution. element + compound: SR Br2(l) + 2NaI(aq) 2NaBr + I2 Example Calcium metal is heated strongly in nitrogen gas. 2 elements: S N2(g) + 3Ca(s) Ca3N2 Liquid water is decomposed through electrolysis. 1 compound: D 2H2O(l) 2H2(g) + O2(g) Ch. 8 Chemical Equations and Reactions 8.3 Activity Series Activity Series Activity ability of an element to react easier it reacts, higher the activity activity series list of elements organized according to activities from highest to lowest Activity Series metals greater activity, easier to lose electrons easier to become a cation nonmetals greater activity, easier to gain electrons easier to become an anion Activity Series used to predict whether single replacement reactions will occur most an active is on top element can replace anything below it but not any above it Practice zinc and hydrofluoric acid calcium copper and lead (II) nitrate and lithium sulfate bromine and iron (II) chloride