Lecture_13 - Today's Lecture Energy, Enthalpy, and...

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1 Energy, Enthalpy, and Thermochemistry Today’s Lecture 9.4 Calorimetry 9.5 Hess’s Law 9.6 Standard Enthalpies of Formation 9.7 Sources of Energy (Omit) 9.8 New Energy Sources (Omit) 1 Calorimetry ± calorimetry is the science of measuring heat ± is based on observing the temperature change when a body absorb or discharges energy a hea body absorbs or discharges energy as heat ± heats of reactions are experimentally determined in a calorimeter ± note that substances respond differently to heating (e.g. we have already talked about the response of ideal gases 2 to heating) ± in general terms, the heat capacity (C) of a substance is defined as e temperatur in increase absorbed heat (C) Capacity Heat =
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2 Calorimetry (cont’d) ± when heating a substance, the energy required to reach a certain temperature will depend on the amount of substance present thus in defining heat capacity the capacity, amount of substance is required ± if heat capacity is given per gram of substance, it is called the specific heat capacity with units of J K -1 g -1 or J o C -1 g -1 ± if heat capacity is given permole of substance, it is 3 called the molar heat capacity with units of J K -1 mol -1 or J o C -1 mol -1 ± s e eT ab l e9 .3f o rt h es p e c i f i ch e a tc a p a c i t i e so fs om e common substances Types of Calorimeters ± the “coffee-cup” calorimeter ± constant-pressure calorimetry ± measures the change in enthalpy of the reaction ( Δ H=q P ) ± for reactions involving solutions (see example 9.3), the total volume essentially remains constant throughout the reaction thus Δ V = 0 ( e no PV 4 reaction thus, V = 0 (i.e. no PV work occurs and q p = Δ H= Δ E) ± for reactions involving gases, Δ Hand Δ E
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Lecture_13 - Today's Lecture Energy, Enthalpy, and...

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