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Problem_Set_4_SolutionsFall2008

# Problem_Set_4_SolutionsFall2008 - 20.110 Problem Set 4...

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20.110 Problem Set 4 Solutions 1.) Calculate Δ A reaction ° and Δ G reaction ° for the reaction CH 4 ( g ) + 2O 2 ( g ) CO 2 ( g ) + 2H 2 O( l ) at 298 K from the combustion enthalpy of methane and the entropies of the reactants and products. All reactants and products are treated as ideal gases ( ) ( ) ( ) ( ) 2 2 4 2 1 1 1 1 1 1 1 1 1 1 3 CO , 2 H O, CH , 2 O , 213.8 J mol K + 2 70.0 J mol K 186.3 J mol K 2 205.2 J mol K 242.9 J mol K 890.3 10 J m combustion combustion combustion combustion combustion G H T S S S g S l S g S g G - - - - - - - - - - Δ = Δ - Δ Δ = + - - = × - - × = - Δ = - × o o o o o o o o o ( ) 1 1 1 3 1 ol 298.15 K 242.7 J mol K 818.6 10 J mol - - - - - × - = - × ( ) ( ) combustion combustion combustion combustion combustion combustion combustion combustion combustion combustion A U T S H PV T S G T S PV T S G nRT Δ = Δ - Δ = Δ - Δ - Δ = Δ + Δ - Δ - Δ = Δ - Δ o o o o o o o o o ( ) 3 1 1 1 3 1 where is the change in the number of moles of gas phase species in the reaction 818.6 10 J mol 2 8.314J mol K 298.15 K 813.6 10 J mol combustion n A - - - - Δ = - × - - × × Δ = - × o 2. ) The standard Gibbs energy of formation Δ G f ° for carbon dioxide gas is –394.4 kJ mol –1 . Calculate the Gibbs energy of formation of carbon dioxide at its normal sea level partial pressure of 0.00031 atm. The Gibbs energy of formation is given by: ( ) ( ) ( ) ( ) ( ) ( ) ( ) ( ) 0 0 f f 0 -1 -1 -1 -1 p Δ G p Δ G p n R Tln p 0.00031 atm 394.4 kJ mol 1 mol 8.314472 J K mol 298 K ln 0.99969 atm 414.4 kJ mol   = +     = - + × × = - 3.) Many biological macromolecules undergo a transition called denaturation. Denaturation is a

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process whereby a structured, biological active molecule, called the native form, unfolds or becomes unstructured and biologically inactive. The equilibrium is native folded ( ) ° ° ° ° ° ° denatured unfolded ( ) For a protein at pH = 2, the enthalpy change associated with denaturation is Δ H ° = 418.0 kJ mol
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