Chapter 6Chapter 6 First Law of Thermodynamics• Systems– Open (human)– Closed (ice pack; closed bottle)– Isolated (Na metal under vacuum)Work and Energy• Work is movementagainst an opposingforce.• w = f x d– 1 J = 1 kg m2 s-2• Internal Energy (U) isthe capacity of a systemto do work.• ∆U = wInternal EnergyPotentialEnergyKineticEnergytranslationalrotationalvibrationalHeat• Heat is energy transferred as a result of atemperature difference.– 1 cal = 4.184 J• In an adiabatic (not passing through)system:– ∆U = w• Nonadiabatic (diathermic):– ∆U = q (heat)The first law o f thermodynamics ∆Uqw=+State function(depends only on stateAnd not path)Not state functionsExpansion work PfAfPAwfdPAdwP VwPVPwexexexexex===×= ×== −==∆∆expanding in vacuum & 00Reversible, isothermal expansiondw PdVwPdVPV nRTwnRTdVVwnRTVVPVwnRTPPVVVVfiififif= −= −== −= −== −∫∫From ideal gas law, Using Boyle's law : constantlnlnCalorimetry• Transfer of heat is measuredwith a calorimeter.– Exothermic– Endothermic• qcal = Ccal ∆T, and q = qcal• Calibrate the calorimeter bydetermining Ccal.• Specific heat capacity, Cs =C/m J 0C-1 g-1.The Power of Chemical Reactions• Reactions can be endothermic (absorb heatfrom the surrounding) or exothermic(release heat into the surrounding).The Power of Chemical Reactions• Reactions can be endothermic (absorb heatfrom the surrounding) or exothermic(release heat into the surrounding).Enthalpy H = U + PV• Change in enthalpy of a system is equal tothe heat released or absorbed at constantpressure.• ∆H = ∆U + P∆V• ∆H = q + w + P∆V• ∆H = q - Pex∆V + P∆V• Since system is open to the atmosphere,– Pex = P, and ∆H = q• ∆H > 0 endothermic, and ∆H < 0 exothermicCP & CV CqTUq HqCUTCHTHUnRTCUnRTTUTnR C nRCCRvpPvpm vm======+=+=+=+=+∆∆∆∆∆∆∆∆∆ ∆∆∆∆∆∆@ constant volume, @constant pressure, ,,Enthalpy of Physical Change ∆Hvap = Hm(vapor) - Hm(liquid) ∆Hfuc = Hm(liquid) - Hm(solid) ∆Hsubl = Hm(vapor) - Hm(solid)Standard Reaction EnthalpiesCH O g CO H O g lgg42 2 222() ()() ()/()+ → +Combining Reaction Enthalpies:Hess’s Law• The overall reaction enthalpy is the sum of thereaction enthalpies of the steps into which thereaction can be divided.Given : - 23 kJ - 39 kJ +18 kJCalculate : ?Fe O CO Fe COFe O CO Fe O COFe O CO FeO COFeO CO Fe CO23 223 34 234 22323323+ → ++ → ++ → ++ → +Standard Enthalpy of formation(∆Hf0)∆Σ∆ Σ∆HnH nHrf f00 0= −() ()products reactantsThe Born-Haber CycleAllows the calculation oflattice enthalpy, which is thestrength of interactionbetween ions.437+89+122+418-349-∆HL=0∆HL = +717 kJ mol-1Bond