Enthalpy Chapter 2.2

(2.2) enthalpy enthalpy enthalpy thermodynamic state function defined by: H=E+PV changes informal non thalpy (AH) can be measured in @constant pressure: \(\Delta H=\Delta E+P\Delta V\) \[\Delta M=\{A+w\}+PaV\] recall that \(\Delta E=q+w~I\) that \(wV=-D\Delta V\rightarrow\triangle W=(q-rav)+P\Delta V\) \(+\Delta H=q_{r}\) ΔH is equal to heat (q.) Howing into systrom physical procusses & latent heat →latent heat is the energy change change associated will physical processes that involve change! of state PACE ESS himp is ENDOTHERMIC melling (haion), boiling (vapourization), sublimation consume enagy conciant (-) EXOTHERMIC condensation, freezing, deposition energy release energy energy added breat → if constant pressure, the latent heat values are also Att values forward & reverse processes have the same q valve but opposite signs not standard conditions ENTHALPY UNDER STANDARD CONDIΠΟΝΣ \(\Delta H^{*}\) →in the study of thermodynamics, standard conditions are: 1 atm (101.525 xpa) $ 25°C (298.15k), unless otherwise stated \(\Delta H^{*}\) where denotes under standard conditions \(\triangle H\) for chemical reactions \[\longrightarrow\Delta H_{rxn}=\Sigma H(productr)-\sum H(reactanHr)\] if a run releases heat, it's exothermic system's if a ren absorbs heat, it's endothermic, system gains lost energy. DHCO energy energy. \[\Delta H>0\] units of reaction enthalpies → when \(\Delta{H^{*}}_{rm}\) is shown in KJ, the enthalpy change For the ran involving the Its of moles equal to the stoichiometeric coefficients of the balanced egn as written KJ value of \(\triangle H_{nen}^{*}\) is proportional to stoich coefficients (12) \(H_{2}(g)+Y_{2}O_{2(g)}\rightarrow H_{1}O_{(g)}\) \[2H_{x(y)},O_{xy)}\rightarrow2H_{x}O_{yy}\] \[{\Delta H^{*}}_{ros}=-2+2~B\] when ΔH°rm is shown in kJ mol⁻¹, it means the enthalpy change for the ranper 1 moleeither stated or implied always write rin so substance in question has stoich coefficient of 1 (14) H₂(g) + ½O₂(g) → H₂O (g) ΔH°rm = -242 kJ mol⁻¹ → enthalpy change for O₂ in this ran is -484 kJ mol⁻¹ above 2 ways of reporting ΔH°rm are equivalent measurement of ΔH calorimetry is used to study heat flow of chemical & physical processes (SIMPLE CALORIMETER) "system" - calorimeter; "surroundings" - universe the calorimeter is an isolated system "system" made up of chemical reactants (ran), solvent, dry calorimeter assembly The Redarma Solution within the system, heat flows from reactants to the solvent to the calorimeter (or vice versa) denote heat gained by gren, gens, qual →gron = -(9:01 + qua) if calorimeter has O heat capacity →heat absorbed/released by solwent can relate to heat capacity 9:01 = Moul ( ΔΤου •if@constant pressure, the geen value is also AH value under standard conditions, the grim value is the standard enthalpy change (AH°) value MOLAR ENTHALPY OF RXN → express ΔH as amount of energy per 1 mole of particular substance → resultant value of ΔH is the molar enthalpy of rxn → always refers to specific species in rxn CALORIMETER CALIBRATION → heat absorbed / released by calorimeter needs to be taken into account (qcal) qrxn = -(qsol + qcal) Ccal (Cue calorimeter calibration) 2 methods for calorimeter calibration add known hot water to known temperature heat lost by water is absorbed by calorimeter measure temp @ eqm. qwater = -qcal Ccal = - (mwater * Cwater * ΔTwater) / ΔTcal carrying out chemical rxn, w/ known heat. heat released by rxn absorbed by calorimeter qcal = Ccal * ΔTcal = -qrxn Ccal = - (qrxn / ΔTcal) **BOMB CALORIMETER** used to measure heat liberated from gaseous / combustion rxns vessel ("bomb") immersed in water takes → necessary to calibrate, determine Ccal → rxns under constant volume, measured heat transfer corresponds to ΔE negligible volume change, calorimeter has excess oxygen pressure change is negligible → heat transfer is equal to ΔH → amount of heat produced by chemical rxn in a bomb calorimeter: qrxn = - (qwater + qcal) = - (Ccal + Ccalwater * mcalwater) * ΔT