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The Richard Stockton College of New Jersey
Chemistry Program, Division of Natural Sciences and Mathematics PO Box 195, Pomoma, NJ
CHEM 3410: Physical Chemistry I — Fall 2007
Exam 2
November 16, 2006
8:30–9:45 AM
Name: Read all of the following information before starting the exam:
- This is a closed book exam. You are permitted an aid sheet consisting of two sides of a 8.5” x 11” piece of paper. Your aid sheet must be turned in with your exam.
- Show all work, clearly and in order, if you want to get full credit. I reserve the right to take off points if I cannot see how you arrived at your answer (even if your final answer is correct).
- Please keep your written answers brief; be clear and to the point. I will take points off for rambling and for incorrect or irrelevant statements.
- Justify your answers. Clearly state any assumptions you make.
- You have 75 minutes to complete the exam.
- Be sure to read all the questions first. You do not have to complete the problems in any particular order.
- Good luck!
Use of wireless communication devices at any time
during the exam is strictly prohibited.
Question Score Total
1 15 2 15 3 20 4 20
Total 70
- ( 15 points) For the isomeric conversion reaction n-butane ⇀↽ iso-butane, the equilibrium constant Kp is 0.686 at 450 K and 0.858 at 500 K.
(a) Without doing any computations, do you expect this reaction to be exothermic or endothermic? Briefly explain your answer. ( 8 )
(b) Use this data to calculate the enthalpy of this reaction. State any assumptions you make to solve this problem. ( 7 )
- ( 20 points) Consider the reaction:
CO(g) + 2 H 2 (g) ⇀↽ CH 3 OH(g)
You are given the following data:
∆H rxn◦ = − 90 .2 kJ/mol ∆S rxn◦ = − 219 .1 J/mol·K
(a) Find ∆G◦ rxn and Kp at 500 K for the reaction. You may assume that both ∆H rxn◦ and ∆S◦ rxn are independent of T. ( 5 )
(b) Write an expression of Kp in terms of the partial pressures of the species involved in the reaction. Feel free to omit the reference pressure for convenience. ( 3 )
(c) Starting from your expression in part (b), write Kp in terms of the mole fraction of each species and the total pressure, Ptot. You may use a relationship we derived in class or the following relationship between the partial pressure (Pi) and mole fraction (Xi) of a species may be useful:
Pi = XiPtot
( 3 )
(d) In a particular experiment, you begin with 1 mole of CO(g) and 1 mole of H 2 (g). The reactants are allowed to react to form CH 3 OH(g) at 500 K and at constant total pressure Ptot. What is Ptot if at equilibrium 0.25 moles of CH 3 OH(g) are formed?
CO(g) + 2 H 2 (g) ⇀↽ CH 3 OH(g)
( 5 )
(e) Suppose that the yield of CH 3 OH(g) needs to be increased to 0.3 mole. Should the pressure be increased, decreased, or not changed compared to the pressure in part c. Explain briefly. (No calculation is required). ( 4 )
Potentially useful information
R = 0.0821 L·atm/mol·K = 8.314 J/mol·K
P V = nRT for an ideal gas
∆G = ∆H − T ∆S
For the equation ax^2 + bx + c = 0 solutions have the form:
x =
−b ±
b^2 − 4 ac 2 a
