Thermochemistry: Energy Flow and Chemical ChangeThermochemistry:Energy Flow and Chemical ChangeForms of Energy and Their InterconversionEnthalpy:Heats of Reaction and Chemical ChangeCalorimetry:Laboratory Measurement of Heats of ReactionStoichiometry of Thermochemical EquationsHesss Law of Heat SummationStandard Heats of Reaction (H0rxn)Thermochemistry is a branch of thermodynamics that deals withthe heat involved with chemical and physical changes.Thermodynamics is the study of heat and its transformations.Fundamental premiseWhen energy is transferred from one object to another, it appears as work and/or as heat.For our work we must define a system to study;everything elsethen becomes the surroundings.A chemical system and its surroundings.the systemthe surroundingsE = Efinal- Einitial= Eproducts- EreactantsEnergy diagrams for the transfer of internal energy (E) between a system and its surroundings.Heat and work: two forms of energy transferHeat (thermal energy, q) energy transferred between a system and its surroundings as a result of a difference in their temperatures only.Work (w) energy transferred when an object is moved by a force.E = q + wNumerical values of q and w can be positive and negativeEnergy coming in to the system is +.Energy going out from the system is -.A system transferring energy as heat only.A system losing energy as work only.Energy, EZn(s) + 2H+(aq) + 2Cl-(aq)H2(g) + Zn2+(aq) + 2Cl-(aq)E>> PV.H = E + PVwhere H is enthalpyEnthalpy diagrams for exothermic and endothermic processes.Enthalpy, HEnthalpy, HCH4+ 2O2CO2+ 2H2OHinitialHinitialHfinalHfinalH2O(l)H2O(g)heat out heat inH < 0 H > 0AExothermic process BEndothermic processCH4(g) + 2O2(g) CO2(g) + 2H2O(g) H2O(l) H2O(g)H = Hfinal Hinitial= Hproducts- HreactantsDrawing Enthalpy Diagrams and Determining the Sign of HPROBLEM: In each of the following cases, determine the sign of H, state whether the reaction is exothermic or endothermic, and draw and enthalpy diagram.(a) H2(g) + 1/2O2(g)H2O(l) + 285.8kJ(b) 40.7kJ + H2O(l) H2O(g)Specific Heat Capacities of Some Elements, Compounds, and MaterialsSpecific Heat Capacity (J/g*K)Substance Specific Heat Capacity (J/g*K)SubstanceCompoundswater, H2O(l)ethyl alcohol, C2H5OH(l)ethylene glycol, (CH2OH)2(l)carbon tetrachloride, CCl4(l)4.1842.462.420.864Elementsaluminum, Algraphite,Ciron, Fecopper, Cugold, Au0.9000.7110.4500.3870.129woodcementglassgranitesteelMaterials1.760.880.840.790.45Finding the Quantity of Heat from Specific Heat CapacityPROBLEM: A layer of copper welded to the bottom of a skillet weighs 125 g.How much heat is needed to raise the temperature of the copper layer from 250C to 300.0C?The specific heat capacity (c) of Cu is 0.387 J/g*K.Use q = (m)(c)(T)Finding the Quantity of Heat from Specific Heat CapacityPROBLEM: Find the heat transferred in kJ when 5.50 L of ethylene glycol (density = 1.11 g/mL, c = 2.42 J/g*K) in a car radiator cools from 37.0 oC to 25.0 oC.Coffee-cup calorimeter.Sample Problem 6.4 Determining the Heat of a ReactionPROBLEM: A 10.25 carat (1 carat = 0.2000 g) diamond is heated to 74.21 oC and immersed in 26.05 g of water in a constant pressure calorimeter. The initial temperature of the water is 27.20 oC. Calculate the T of the water and of the diamond (cdiamond= 0.519 J/g*K, cwater= 4.184 J/g*K).AMOUNT (mol)of compound AAMOUNT (mol)of compound BHEAT (kJ)gained or lostmolar ratio from balanced equationHrxn(kJ/mol)Summary of the relationship between amount (mol) of substance and the heat (kJ) transferred during a reaction.Using the Heat of Reaction (Hrxn) to Find AmountsPROBLEM: The major source of aluminum in the world is bauxite (mostly aluminum oxide).Its thermal decomposition can be represented by If aluminum is produced this way, how many grams of aluminum canform when 1.000x103 kJ of heat is transferred?Al2O3(s) 2Al(s)+3/2O2(g) Hrxn= 1676 kJUsing the Heat of Reaction (Hrxn) to Find AmountsPROBLEM: Using the following equation, if 137 kJ is given off per mole of C2H4reacting, how much heat is released when 15.0 kg of C2H6forms?C2H4+H2C2H6Using Hesss Law to Calculate an Unknown HPROBLEM: Two gaseous pollutants that form in auto exhaust are CO and NO.An environmental chemist is studying ways to convert them to less harmful gases through the following equation:CO(g)+NO(g) CO2(g)+ 1/2N2(g) H = ?Given the following information, calculate the unknown H:Equation A:CO(g) + 1/2O2(g) CO2(g) HA= -283.0 kJEquation B:N2(g) + O2(g) 2NO(g) HB= 180.6 kJSelected Standard Heats of Formation at 250C(298K)Formula H0f(kJ/mol)calciumCa(s)CaO(s)CaCO3(s)carbonC(graphite)C(diamond)CO(g)CO2(g)CH4(g)CH3OH(l)HCN(g)CSs(l)0-635.1-1206.901.9-110.5-393.5-74.9-238.613587.9hydrogennitrogenoxygenFormula H0f(kJ/mol)H(g)H2(g)N2(g)NH3(g)NO(g)O2(g)O3(g)H2O(g)H2O(l)Cl2(g)HCl(g)000-92.30218-45.990.3143-241.8-285.8107.8Formula H0f(kJ/mol)silverAg(s)AgCl(s)sodiumNa(s)Na(g)NaCl(s)sulfurS8(rhombic)S8(monoclinic)SO2(g)SO3(g)000-127.0-411.12-296.8-396.0Gas = 1 atmAqueous solution = 1 MPure substance = most stable form at 1 atm and 298 KWriting Formation EquationsPROBLEM: Write balanced equations for the formation of 1 mol of the following compounds from their elements in their standard states and include H0f.(a) Silver chloride, AgCl, a solid at standard conditions.(b) Calcium carbonate, CaCO3, a solid at standard conditions.(c) Hydrogen cyanide, HCN, a gas at standard conditions.The general process for determining H0rxnfrom H0fvalues.Enthalpy, HElementsReactantsProductsH0rxn= mH0f(products)- nH0f(reactants)decomposition-H0fH0fformationH0rxnHinitialHfinalCalculating the Heat of Reaction from Heats of FormationPROBLEM: Nitric acid, whose worldwide annual production is about 8 billion kilograms, is used to make many products, including fertilizer, dyes, and explosives.The first step in the industrial production process is the oxidation of ammonia:Calculate H0rxn from H0f values.H0fNH3 (g)= -45.9 kJ/molH0fO2 (g)= 0 kJ/molH0fNO(g)= 90.3 kJ/molH0fH2O(g)= -241.8 kJ/mol4NH3(g)+5O2(g) 4NO(g)+6H2O(g)