Chapter Outline 4/28/2014. P-V Work. P-V Work. Isolated, Closed and Open Systems. Exothermic and Endothermic Processes. E = q + w

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1 Islated, Clsed and Open Systems 9.1 Energy as a Reactant r a Prduct 9.2 Transferring Heat and Ding Wrk 9.5 Heats f Reactin and Calrimetry 9.6 Hess s Law and Standard Heats f Reactin 9.7 Heats f Reactin frm Heats f Frmatin and Bnd Energies 9.8 Mre Applicatins f Thermchemistry pen systems can exchange mass and energy clsed systems can nly exchange energy islated systems can nt exchange mass r energy Exthermic and Endthermic Prcesses P-V Wrk Exthermic prcess: Heat flws ut f the system t surrundings (q < 0). Endthermic prcess: Heat flws int the system frm surrundings (q > 0). internal energy E = q + w Heat flw Wrk (F x d) E > 0 when heat flws in (q > 0) r wrk is perfrmed n the system (w > 0) E < 0 when heat flws ut (q < 0) r wrk is perfrmed n the surrundings P-V Wrk Wrk = P x V P = F A (a) Intake (b) Cmpressin (c) Pwer (expansin) (d) exhaust 1

2 Sample Exercise 9.2: Calculating P-V Wrk Sample Exercise 9.3: Relating E, q, and w A tank f cmpressed helium is used t inflate 100 ballns fr sale at a carnival n a day when the atmspheric pressure is 1.01 atm. If each balln is inflated with 4.8 L, hw much P-V wrk is dne by the cmpressed helium? Express yur answer in Jules. The racing cars in the figure are pwered by V8 engines in which the mtin f each pistn in its cylinder displaces a vlume f L. If cmbustin f the mixture f gasline vapr and air in ne cylinder releases 1.68 kj f energy, and if 33% f the energy des P-V wrk, hw much pressure, n average, des the cmbustin reactin mixture exert n each pistn? Hw much heat flws frm the reactin mixture t its surrundings? 9.1 Energy as a Reactant r a Prduct 9.2 Transferring Heat and Ding Wrk 9.5 Heats f Reactin and Calrimetry 9.6 Hess s Law and Standard Heats f Reactin 9.7 Heats f Reactin frm Heats f Frmatin and Bnd Energies 9.8 Mre Applicatins f Thermchemistry Enthalpy and Enthalpy Changes Many physical and chemical changes take place at cnstant pressure, e.g. bichemical reactins, labratry reactins, etc. The heat flw under cnstant pressure cnditins is called Enthalpy (H) Enthalpy is a measure f the system s ttal energy: H = E + PV H is hard t quantify exactly, but the change in enthalpy H can be easily measured. H = E + P V and it can be shwn that this equal t the heat flw at cnstant pressure q p - Enthalpy Sign Cnventins 9.1 Energy as a Reactant r a Prduct 9.2 Transferring Heat and Ding Wrk 9.5 Heats f Reactin and Calrimetry 9.6 Hess s Law and Standard Heats f Reactin 9.7 Heats f Reactin frm Heats f Frmatin and Bnd Energies 9.8 Mre Applicatins f Thermchemistry 2

3 Endthermic 4/28/2014 Heat Capacity (C p ) Nte: the symbl is upper case Specific Heat (c p ) Nte: the symbl is lwer case The heat required t raise the temperature f an bject 1.0 C (cnstant pressure) Units are J/ C mass independent We will use Heat Capacity later in the chapter when we talk abut calrimetry, as well as in the lab The heat required t raise the temperature f 1 gram f a substance 1 C ( cnstant pressure) Units are J/g C We will be using Specific Heat in the lab Calculating Heat Transfer Within the Same Phase q = m c p T T = T final - T initial J units g C Jules g C Sign Cnventins T = T final - T initial If T final < T initial then q < 0 and heat transferred OUT OF bject (EXOTHERMIC) If T final > T initial then q > 0 and heat transferred INTO bject (ENDOTHERMIC) Phase Changes and Heat Flw H fusin and H vap Exthermic Calculating Heat Transfer Acrss a Phase Bundary Mlar heat f fusin: ΔH fus = heat needed t cnvert 1 mle f a slid at its melting pint t 1 mle f liquid. q = nδh fus Mlar heat f vaprizatin: ΔH vap = heat needed t cnvert 1 mle f a liquid at its biling pint t 1 mle f vapr. q = nδh vap The same sign cnventins apply 3

4 Heating Curves and Heat Capacity Ht Sup n a Cld Day, p. 376 Heating Curves and Heat Capacity Ht Sup n a Cld Day, p. 376 Sample Exercise 9.4: Calculating Heat Transfer Acrss Phase Bundaries Heat Transfer frm One Substance t Anther Cld Drinks n a Ht Day, p. 379 Between perids f a hckey game, and ice-resurfacing machine spreads 3.00 x 10 2 liters f ht (40.0 C) water acrss a skating rink. Hw much heat must the water lse as it cls t its freezing pint, freezes, and further cls t -10 C? Assume that the water is the system, and that its density if g/ml at 40.0 C Sample Exercise 9.5: Calculating a Final Temperature frm Heat Gain and Lss Determining Specific Heat, p. 381 Suppse yu wish t make a glass f freshly brewed iced tea. Yu start with exactly 1 cup (237 g) f ht (100.0 C) brewed tea in an insulated mug and add 2.50 x 10 2 g f ice initially at C. All f the ice melts. What is the final temperature f the tea? Assume that the tea has the same thermal prperties as water. 4

5 Determining Specific Heat, p