Chemical Reactions: Thermochemistry Part 1Chemical Reactions: Thermochemistry Part 1First Law of Thermodynamics: Conservation of EnergyChange in Internal EnergyPractice ProblemHeat, Work, and Changes in EnergyEnergy and EnthalpyExamples of EnthalpyThermochemical EquationsEnthalpy of ReactionThe Hydrogen BalloonExo- vs. Endothermic ReactionsExo- vs. Endothermic DemonstrationHeat Capacity and CalorimetryHow is q Measured?Quantitative Heat CapacityΔH of FormationExample of ΔHfoWhat You Should KnowChemical Reactions:Thermochemistry Part 1CH110 FA11 SAS 1Prepare for Recitation December 1stALEKS Objective 13 due November 29thANGEL Quiz 13, December 1stLecture 37: November 16thLecture 38: November 18th(Thanksgiving Break)Lecture 39: November 28thRead: Ch. 4.6,10.5 (Reactions); 5.3 – 5.7, 8.8 (Thermo)Additional Preparation: Packet Rxns: 12-18BLB 10: 57BLB 5: 4,17,29,37,39, 53,55,83,85; Packet 5: 1-7BLB 8: 65a,67ac,92a; 18: 72ab,74; Packet 8: 12-14CH110 FA11 SAS 2By the end of Today’s Lecture you should know:First Law of ThermodynamicsHeat, work, Energy, and EnthalpyThermochemical EquationsHeat of FormationKEY QUESTIONS: THE BIG PICTUREChemical Reactions:Thermochemistry Part 1How can chemical thermodynamics help me to understand the energy of reactions?What is enthalpy and why is it often more useful than energy in chemistry?Remember: Energy is stored in molecules. How can we use it?What is the relationship between a balanced chemical equation and a thermochemical equation?How do thermochemical equations help me understand reaction chemistry?First Law of Thermodynamics:Conservation of EnergyCH110 FA11 SAS 3KINETICENERGYPOTENTIALENERGY• mechanical(moving mass ½ mv2)[ joule = kg m2/s2]• mechanical(mass in a placewhere force can act)• chemical (bonds)• nuclear(binding energy)• electrical(moving charge)• light (photons)• sound (moleculesmoving uniformly)• heat (moleculesmoving randomly)Energy ______ converted from oneform to anotherWhen it is converted, the total energy_______________Change in Internal EnergyCH110 FA11 SAS 4∆E = Efinal– Einitial∆E is a state functionSystem SurroundingsenergySurroundings Systemenergy• Energy is conseved: All energy lost by a system under observation is gained by the surroundingsState function: • Internal energy is the capacity to:• Thermal energy ( _____ ) is energy transferred due to difference in temperaturePractice ProblemCH110 FA11 SAS 5100 mL of water in a beaker is cooled from 90oC to 25oC. A second 100 mL of water in a separate beaker is warmed from 1oC to 25oC. Both beakers are open to the atmosphere. Which system has more energy?A) The system that was cooled has moreB) The system that was heated has moreC) They both have the same energyD) I need more information to answer the questionHeat, Work, and Changes in EnergyCH110 FA11 SAS 6∆E = q + w• During energy conversion, some heatis always producedw = P²V+q+q²V = 0w = -pΔv Δv = 0• The work of expansion is very common (Demo: Sublimation of CO2)∆E = q - pΔv What is the sign of w?Which ends up with higher E?Energy and EnthalpyCH110 FA11 SAS 7• During energy conversion, some heatis always produced• When changes occur at constant pressure:∆E = qp+ wexpansion∆H = qp• Change in enthalpy (ΔH) is the quantity of thermal energy transferred to a system at _______________∆H is a state function• ∆H ≈ ∆E if _________________________(for chemical changes, this is usually true)• Formally: ∆E = qp- pΔv∆H = qp=Examples of EnthalpyCH110 FA11 SAS 8• Freezing and meltingadd heat to ice at 0oC and it melts BUT:• Vaporizing and condensingheat water at 100oC and it vaporizesBUT:• Reaction to change chemical composition• Formation of a compound from elements∆Hfusionheat of fusionExamples of physical changes:∆Hvaporizationheat of vaporizationExamples of chemical changes:∆Hfheat of formation∆Hrxnheat of reactionThermochemical EquationsCH110 FA11 SAS 9A balanced chemical equation that alsoincludes the _______________.∆Ho(delta H standard)Na2O2(s) + 2H2O(l) → 2Na++ 2OH–+ H2O2(aq)Sodium peroxide2H2O2(aq) → 2 H2O + O2When bonds are broken energy is _______, so this reaction gives off _____have high conc. of O2cotton has low ignition temperature….so….. flameRemember the demo show?Units of ∆Ho=Enthalpy of ReactionCH110 FA11 SAS 10∆H = H(products) – H(reactants)Endothermic ∆H > 0Exothermic ∆H < 02 H2(g)+ O2(g) → 2 H2O(g) + heat∆Hrxno= – 483.6 kJCharacteristics of Enthalpy(1) Enthalpy is an extensive property(2) ∆H for a reaction depends on states ofreactants and products (3) ∆H for a reaction is _____ in magnitude but ________ in sign to ∆H for reverse reactionThe Hydrogen BalloonCH110 FA11 SAS 112 H2(g) + O2(g) 2H2O(g) ΔHrxno= -483.6 kJ The reaction to form water from hydrogen and oxygen is _____ thermic.How much heat is given off per mole of H2consumed in the production of water?How much heat is given off per mole of O2consumed in the production of water?The reaction to form H2and O2gas from water vapor is _____ thermic.How much heat will be needed to convert 9g of water vapor into H2and O2gas?Exo- vs. Endothermic ReactionsCH110 FA11 SAS 122 HI(g) productsH2(g) + I2(g) reactantsH∆Hrxn= 53 kJ______THERMIC REACTIONCH4(g) and 2 O2(g) reactantsCO2(g) + 2 H2O(l) productsH∆Hrxn= –890 kJ______THERMIC REACTIONExo- vs. Endothermic DemonstrationCH110 FA11 SAS 13Ba(OH)2•8H2O(s) + 2 NH4(SCN)(s) →Ba(SCN)2(aq) + 2 NH3(g) + 10 H2O(l)• mix two solids• highly endothermic reaction• increase in entropy is driving force• go from two ordered crystals to ionsand gases in solutionEndothermicExothermicNa2SO3(aq) + NaOCl(aq) →Na2SO4(aq) + NaCl(aq) • highly exothermic reaction• oxidation/reduction drives the reaction(can you identify this?)Heat Capacity and CalorimetryCH110 FA11 SAS 14Experimental measurement of heat flowFor H2O: C= 4.184 Jg °Cq = m C ∆Theat surroundings = (conservation of energy)mc∆Tsurroundings= So…temperature increase in the surroundings means heat is ________ by system (and vice versa).Measure ∆T for surroundings in a controlled environment (calorimeter)How is q Measured?CH110 FA11 SAS 15Quantitative Heat CapacityCH110 FA11 SAS 16A calorimeter with 200 g H2O is used for reaction. If T rises from 25.0oC to33.0oC, how much energy is released ?(heat capacity of H2O(l) = 4.184 J/ oC g)ΔH of FormationCH110 FA11 SAS 17ElementscombineCompoundWhen all substances
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