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Chem 161-2010 Lecture 11

# Chem 161-2010 Lecture 11 - CHEMISTRY 161-2010 LECTURE 11...

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CHEMISTRY 161-2010 LECTURE 11 ANNOUNCEMENTS E-MAIL ATTENDANCE EXAMS Chem 161-2009 recitation 14 th week 1

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PLAN FOR TODA Y : CHAPTER 6 (sections 6.5-6.6): CALORIMETRY AND HEAT CAPACITY HESS’S LAW Chem 161-2009 recitation 14 th week 2
CHAPTER 6 RELEVANT EQUATIONS ∆E = ΔU = q + w 1 Latm = 101.3 J Pressure-volume work: w = -PΔV; therefore, ∆E = q –P∆V Non-pressure-volume work: w = F x d (note, using a piston and cylinder, the piston has to move); F = m x a; w = m x a x d = m x g x d Units of non-pressure-volume work: m in kg, g = 9.81 m x s -2 , d in m; Units: kg x ms -2 x m = kgm 2 s -2 = J Heat Capacity = C = q/ΔT molar heat capacity = C/mol = q/(ΔT x mol) Specific Heat Capacity = SHC = SH = C/g = (q/ΔT)/g = q/ΔTg q = SHC x ΔT x g SHC H2O = 4.18J/g o C First law of thermodynamics: Energy is neither created nor destroyed. Therefore, heat lost by one = the heat gained by other. -q 1 = +q 2 Hess’s Law : ΔH is a state function, so path not important. Rules for changing enthalpy equations: o If the enthalpy equation is reversed, sign of ΔH is reversed. o If the enthalpy equation is halved, quantity of ΔH is halved. o If the enthalpy equation is doubled, quantity of ΔH is doubled. Enthalpy of Formation (more correctly, “Standard enthalpy of formation”) = ΔH o f o is for formation of one mole of product o from its elements o all reactants (i.e., elements) and products in their standard states (1 atm & 298K) o all elements in their most stable form, e.g., oxygen = O 2(g) ; mercury = Hg (l) ; sodium = Na (s) o ΔH o f of elements = 0 Enthalpy of reaction : o ΔH o Rx = ∑n p ΔH o f,products - ∑n r ΔH o f,reactants Chem 161-2009 recitation 14 th week 3

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CALORIMETRY AND HEAT CAPACITY C = q/ΔT Heat capacity = amount of heat energy required to raise the temperature 1 o C. ET: An analogy for heat capacity is volume capacity. Compare two bathtubs, one having a volume capacity of 150 gallons until reaching an end point (overflowing), while the other has a smaller volume capacity of only 75 gallons; correspondingly, heat capacity is the quantity of heat that can be put in until the temperature increases by 1 o C. ET: Discuss heat capacity of H 2 O and iron at the beach; Any increase in q, that does not contribute to a corresponding increase in T, results in an increase in HC. o If energy goes into increased vibration of bonds, or increased rotation of molecules then the temperature doesn’t rise; hence, large molecules have a greater C than small molecules because more energy goes into vibration and rotation than small molecules; H 2 O has a greater C than Fe (energy goes into vibrations, rotations, and breaking H bonds, not just into translational energy). ET: Discuss SHC = HC/g. (Specific density = g/ml; Specific volume = volume/g) ET: Discuss molar HC = HC/mol Specific heat capacity calculation – Simple Hill & Petrucci 45a. How much heat, in kilojoules, is required to raise the temperature of 320.0 g water from 15.0 to 96.0 o C?
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Chem 161-2010 Lecture 11 - CHEMISTRY 161-2010 LECTURE 11...

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