CHEM 1211 Lecture 13Outline of Last Lecture I. Acid Concentrations1. Example One2. Example Two3. Example Three (CQ #1)4. Example Four 5. Example FiveII. Chemical ThermodynamicsA. Heat Transfer1. CQ #22. CQ #33. Example OneB. Internal Energy(NEW THERMODYNAMIC FXN)1. Example OneOutline of Current Lecture I. Table OneII. EnthalpyIII. CalorimetryIV. Hess’s LawCurrent Lecture: When Zn reacts with HCl hydrogen gas…There is a change in enthalpy..U = qp – P V or qp + WpI. Table OneEnergy Transferred Sign Convention Effect on UsystemHeat to system (endo) q > 0 +Heat from system (exo) q < 0 -Work done on system W > 0 +Work done by system W < 0 -II. Enthalpy H°= KJ / mol-rxn1. H2(g) + ½O2(g) 1 H2O(g) H°= -241.8 KJ / mol-rxnIf the fuel tank hold 234,265 lbs. of hydrogen, how much heat is released when it all reacts with oxygen in the tank?1 lb. = 454g ; mm H2= 2.020 g / molq= H° + mol-rxn234,265 lb. 454g H21 mol H21 mol-rxn = 52,652,638.61 mol-rxn lb. 2.020g 1 mol H2q= (-241.8) x 52,652,638.61 = -1.27 x 1010 KJ: exothermic rxnIII. Calorimetry1. Ammonium Chloride is very soluble in H2O. When 4.50g NH4Cl is dissolved in 53.00g of H2O, the temperature of the solution decreases from 20.40°C to 15.72°C. Calculatethe enthalpy of dissolution of NH4Cl (in KJ / mol-rxn). Assume that the specific heat of solution is 4.18 J/ g°C and that calorimeter constant is 26.71 J/°C(mm NH4Cl: 53.490 g/mol)NH4Cl(s) NH4+(aq) + Cl-(aq) : The system at constant pressure-qsystem = qcal + qsoln** work = o, only exists when a gas is formed** T < 0, process is endothermic T =( 15.72°C – 20.40°C) = -4.68M= 53g H2O + 4.50g NH4Cl = 57.50 g solnQsoln = mC T =57.50g x 4.18 J/mol°C x -4.68°C = -1124.8 J Qcal= Ccal T = 26.71 J/°C x -4.68°C = -125.0JQsystem = -(qcal + qsoln) = + 1249.8 JMol-rxn: 4.50g NH4Cl 1 mol NH4Cl 1mol-rxn = 0.084127 mol-rxn 53.49g NH4Cl 1 mol NH4Cl Hdiss = +1249.8 = 14,856.11 J = 14.9 KJ : Endothermic! 0.084127 mol-rxn mol-rxnIV. Hess’s Law: Law of heat summationEnthalpy = state functionH°= H°a + H°b + H°c … etcThe enthalpy change for a rxn is the same whether it occurs by one step or by any series of
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