Exam1A

Exam1A - Name: _ Date: _ VERSION A Part 1. Calculation and...

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Name: __________________________ Date: _____________ VERSION A Part 1. Calculation and Short Answer Problems. All work for the following questions must be done in THIS TEST BOOKLET. Calculations done with no shown work will receive zero points. Your work must be clear and logical AND SHOWN to receive maximum (or any) credit. A.Consider the reaction between hydrogen gas and iodine vapor. H 2 (g) + I 2 (g) 2HI(g) H f ˚ (I 2 ) = 62.24 kJ/mol; H f ˚ (HI) = 26.0 kJ/mol S m ˚ (I 2 ) = 261.0 J/(mol K); S m ˚ (H 2 ) = 131.0 J/(mol K); S m ˚ (HI) = 206.0 J/(mol K) a) Calculate the standard enthalpy change for the reaction. (12 points) H r ˚ = n H f ˚ (products) - n H f ˚ (reactants) = (2 ) H f ˚ (I 2 ) – [(1) H f ˚ (H 2 ) +(1) H f ˚ (I 2 )] = (2)(26.0 kJ/mol) – [(1)(0 kJ/mol) + (1)(62.24 kJ/mol)] = –10.24 kJ/mol b) Calculate the standard entropy change for the reaction. (12 points) S r ˚ = nS m ˚ (products) – nS m ˚ (reactants) = (2)S m ˚ (HI) – [(1)S m ˚ (H 2 ) + (1) S m ˚ (I 2 )] = (2)(206.0 J/(mol K)) – [(1)(131.0 J/(mol K) + (1)(261.0 J/(mol K)] = 20.0 J/(mol K) c) Calculate the standard free energy change for the reaction at 25 ºC. (12 points) G r ˚ = H r ˚ – T S r ˚ = –10.24 kJ/mol – (298 K)(20.0 J/(mol/K))(kJ/1000 J) = –16.2 kJ/mol d) Will HI(g) form spontaneously? (2 points) Yes

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This note was uploaded on 01/31/2010 for the course CHEM CHEM 6B taught by Professor Christinajohnson during the Spring '07 term at UCSD.

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Exam1A - Name: _ Date: _ VERSION A Part 1. Calculation and...

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