Chem 141 Chapter 6

Chem 141 Chapter 6 - 6-1Chemistry 141Summer 2008Silberberg...

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Unformatted text preview: 6-1Chemistry 141Summer 2008Silberberg Chapter 6Dr. Ben Tovrog6-2Thermochemistry: Energy Flow and Chemical Change6.1Forms of Energy and Their Interconversion6.2Enthalpy: Heats of Reaction and Chemical Change6.3Calorimetry: Laboratory Measurement of Heats of Reaction-Drop bomb calorimeter6.4Stoichiometry of Thermochemical Equations6.5Hesss Law of Heat Summation6.6Standard Heats of Reaction (Hrxn)6-3Silberberg Chapter 6 Problem AssignmentThese problems are for your practice. They will not be collected or graded. Easy and Medium:6.4, 6.6, 6.8, 6.10, 6.15, 6.17, 6.19, 6.22, 6.26, 6.29, 6.33, 6.35, 6.37, 6.39, 6.41, 6.48, 6.50, 6.52, 6.54, 6.58, 6.62, 6.63, 6.65, 6.67, 6.70, 6.72, 6.73, 6.75, 6.77, 6.80, 6.81, 6.83, 6.90, 6.93, 6.109Hard and Very Hard:6.103, 6.105, 6.108, 6.1106-4Thermochemistryis 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 systemto study; everything elsethen becomes the surroundings.The system is composed of particles with their own internal energies (E or U).Therefore the system has an internal energy. When a change occurs, theinternal energy changes.6-5E = Efinal- Einitial= Eproducts- EreactantsFigure 6.2Energy diagrams for the transfer of internal energy (E) between a system and its surroundings.6-6Figure 6.3A system transferring energy as heat only.6-7Figure 6.4A system losing energy as work only.Energy, EZn(s) + 2H+(aq) + 2Cl-(aq)H2(g) + Zn2+(aq) + 2Cl-(aq)E<0work done onsurroundings6-8Table 6.1 The Sign Conventions* for q, wand Eqw+=E++----+++-depends on sizesof qand wdepends on sizesof qand w* For q: + means system gainsheat; - means system losesheat.* For w: + means word done onsystem; - means work done bysystem.6-9Euniverse= Esystem+ EsurroundingsUnits of EnergyJoule (J)Calorie (cal)British Thermal Unit1 cal = 4.18J1 J = 1 kg*m2/s21 Btu = 1055 J6-10Sample Problem 6.1Determining the Change in Internal Energy of a SystemPROBLEM:When gasoline burns in a car engine, the heat released causes the products CO2and H2O to expand, which pushes the pistons outward. Excess heat is removed by the cars cooling system. If the expanding gases do 451 J of work on the pistons and the system loses 325 J to the surroundings as heat, calculate the change in energy (E) in J, kJ, and kcal.SOLUTION:PLAN:Define system and surroundings, assign signs to q and wand calculate E. The answer should be converted from J to kJ and then to kcal.q= - 325 Jw= - 451 JE = q+ w=-325 J + (-451 J) = -776 J-776J103JkJ= -0.776kJ-0.776kJ4.18kJkcal= -0.185 kcal6-11Figure 6.6Two different paths for the energy change of a system.6-12Figure 6.7Pressure-volume work.6-13The Meaning of Enthalpyw= - PVH = E + PVqp= E + PV = HH E in1. Reactions that do not involve gases.1....
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This note was uploaded on 07/30/2008 for the course CHEM 141 taught by Professor Mulfod during the Summer '08 term at Emory.

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Chem 141 Chapter 6 - 6-1Chemistry 141Summer 2008Silberberg...

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