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practice exam3 with solutions

# practice exam3 with solutions - A Calculate the equilibrium...

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A. Calculate the equilibrium constant K for the reaction: 2NO(g) + O 2 (g) = 2NO 2 (g) at P = 1 atm, T = 298K using the following data: compound G f 0 , kJ/mol H f 0 , kJ/mol NO 86.606 90.291 NO 2 51.258 33.095 G = 2 51.258 – 2 86.606 = -70.696 kJ/mol K = exp(- G/RT) = 2.502 10 12 B. Will the equilibrium constant increase or decrease if temperature is increased? Explain your answer. 2 ln / / K T H RT = ∆ H = 2 33.095 – 2 86.606 = -114.392 < 0 (the reaction is exothermic) Therefore ln / 0 K T < : the equilibrium constant will decrease. C. Calculate the equilibrium constant for P=100 atm and T = 298K. Assume that the reactants and the product are ideal gases. ln[K(P,T)/K(P 0 ,T)] = 0 ( ν )ln( / ) i P P ν 2 1 2 1 i = − − = − ln[K(P,T)/K(P 0 ,T)] = 0 ln( / ) P P or K(P,T)/K(P 0 ,T) = 0 / P P

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K(P,T) =K(P 0 ,T) 0 / P P = 100 K(P 0 ,T) = 2.502 10 14 D. Suppose you have initially 1 mole of NO, 1 mole of O 2 and 1 mole of NO 2 . At a later moment, the amount of NO 2 was found to be 1.2 mol. What are the amounts of NO and O 2 at the same time? n(NO 2 )=1+2 ξ=1.2 mol so ξ=0.1 n(NO) = 1 – 2 ξ =0.9 mol n(O 2 )=1- ξ=0.9 mol 2.
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