ProblemSet11 - CHEM 3615 Problem Set #11 Chemical...

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Unformatted text preview: CHEM 3615 Problem Set #11 Chemical Equilibrium Due December 5, 2007 (midnight Wednesday evening under my office door, Hahn 1107) Read Chapter 7. All problems are due at the start of class and will be graded. Graded Problems 1. The equilibrium constant for the dissociation of Br2 (g) at 1600 K is K = 0.255. Calculate the standard reaction Gibbs free energy change at 1600 K. [kJ/mol] Solution: . . 2. The standard Gibbs free energy change for the decomposition reaction of CaCO3 (s) to CaO (s) and CO2 (g) at 1173 K is 0.178 kJ/mol. Calculate the equilibrium constant for the decomposition at 1173 K. [unitless] Solution: . . , . Page 1 of 5 3. Consider the following chemical equilibrium: 3 3 Using the data tables in the back of your textbook, calculate the standard Gibbs free energy and equilibrium constants at (a) 25 C and (b) 50 C. You may assume that the standard enthalpy change for the reaction is independent of temperature. Note that for : 73.66 134.47 . [kJ/mol, unitless for both parts] Solution: (a) . . . (b) . . & / / . / . -- . -- . . / / & . . . . . . . . . . / -- . . / / / . . . , Page 2 of 5 4. For the following reaction in the gas phase: 2 it was found that when Ao = 2.00 mol, Bo = 1.00 mol, Co = 0 mol, and Do = 3.00 mol are mixed together and come to equilibrium at 25 C, the resulting mixture contains 0.79 mol of C at a total pressure of 1.00 bar. (a) Calculate the mole fractions of each species at equilibrium [unitless], (b) Kx [unitless], (c) Kp [unitless], and (d) the standard Gibbs free energy change for the reaction [kJ/mol]. Solution: no,i /mol nf,i /mol (given) ni /mol ni /mol (deduced) nf,i /mol nf,i /mol xi A 2.00 + B 1.00 C 0 0.79 nf,C +0.79 no,C nC 0.79 0.1163 + 2D 3.00 Totals 6.00 - nf,C -0.79 no,A nA 1.21 0.1782 - nf,C -0.79 no,B nB 0.21 0.0309 +2 nf,C +1.58 no,D nD 4.58 0.6745 +0.79 no,total ntotal 6.79 0.9999 (a) Mole fractions: xi = nf,i/nf,total (see table) (b) . . . . . (c) pi = xiptotal (Dalton) (d) . . . . , Page 3 of 5 5. The equilibrium constant for the reaction: 2 is Kp = 1.69 x 10-3 at 2300 K. A mixture consisting of 5.00 g of nitrogen and 2.00 g of oxygen in a container with a volume of 1.00 L is heated to 2300 K and is allowed to come to equilibrium. Calculate the mole fraction of NO at equilibrium. [unitless] Solution: . . ni,o /mol ni /mol ni,f /mol xi N2 (g) 0.1786 -x 0.1786-x . . + O2 (g) 0.0625 -x 0.0625-x . . . . / / . . 2NO (g) 0 +2x 2x . Totals 0.2411 0 0.2411 1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Page 4 of 5 6. Use the data in the back of your book to determine the standard Gibbs free energy change for the following reactions at 298K [kJ/mol]: 2 2 2 2 Indicate in each case if Kp is greater than or less than 1. Solution: (a) . . , -- / # 0 1, 1 . (b) . . , -- / # 0 1, 1 . . Page 5 of 5 ...
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