pv n rt a comparison of h and e comparison and 2nas

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Unformatted text preview: H q p = ∆H ConstantConstant-Pressure Calorimeter Calorimeter CoffeeCoffee-cup calorimeter Relationship between qv and qp ∆E = q + w q p = ∆H At constant Presure: w = - P∆V ∆E = ∆H − P∆V ∆H − ∆E = p∆V q p − qv = p∆V q p ≈ qv For liquid and solid, P∆V is very small: For reactions in which gases involved : PV = nRT q p - qv = P∆V = ∆n ⋅ RT A Comparison of ∆H and ∆ E Comparison and 2Na(s) + 2H 2 O(l) → 2NaOH (aq) + H 2 (g) At constant pressure: ∆H = -367.5 kJ ∆E = q + w = q p - P ∆V = ∆H - P∆V At 25°C and 1 atm: 1 mole H2 = 24.5 L H 2 expanding: w = -P∆V = - (1atm × (24.5-0)L/mol) -P atm = - 24.5L ⋅ atm/mol ×101.3J/L ⋅ atm = - 253.25J/mol ∆E = qP -P∆V = ∆H-P∆V = - 367.5 kJ/mol - 0.25 kJ/mol = - 367.75 kJ/mol Calorimetry Calorimetry Question: Question: Under constantconstantvolume conditions the conditions the heat of combustion (q) of 1 mole liquid benzene benzene , C6H6 (l) , at at 289 289 .15K is 3264kJ, the what is the enthalpy change ( H) of the combustion reaction of liquid benzene C6H6 (l) Combustion reaction of liquid benzene: C6 H 6 (l ) + _O2 ( g ) = _CO2 ( g ) + _H 2O(l ) C6 H 6 (l ) + 15 O2 ( g ) = 6CO2 ( g ) + 3H 2O(l ) 2 ConstantConstant-volume conditions: q v = -3264kJ/mol ∆H = ∆E + p∆V = qv + p∆V For reactions in which gases involved : PV = nRT ∆H = qv + ∆nRT ∆H = q p =q v + ∆n RT = - 3264 ×103 J + (6 - 15/2)mol × 8.3145J/mol ⋅ K × 298.15K = - 3267700 J/mol = - 3267.7kJ/mol Heat Heat Capacity • Heat capacity (C): the amount of heat (q) needed to raise the temperature (∆T) of a system by 1 K or 1 °C (1 K = 1oC) Unit of heat capacity: J/K or J/K or J/°C C = q / ∆T q = C × ∆T Question: Calculate the heat capacity of a bomb calorimeter when bomb 26.38 26.38 kJ of heat raised its temperature from 25.000 °C to 29.857°C Ccalorimeter = q / ∆T = 26.38 kJ / (29.857-25.000) °C=5.431 kJ/ °C Question: Temperature rose when a combustion reaction releasing 5037 J of heat took place inside the former calorimeter. If the Ti is 292.03 K, predict Tf. Ccalorimeter =5.431...
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This document was uploaded on 02/26/2014.

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