xm-1key - MCB 11 Spring 2006 Midterm Examination I- Key M....

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MCB 11 M. D. Alper Spring 2006 February 22, 2006 Midterm Examination I- Key 1. (20 pts) The changes in enthalpy and entropy during a reaction affect the energy difference between the starting materials and the products of that reaction. a. Define the “change in enthalpy” and the “change in entropy” as if to your roommate who knows absolutely nothing about them. The change in enthalpy represents the energy lost or gained in making or breaking bonds. The change is negative when breaking a bond, positive when making a bond. The change in entropy represents the change in the amount of order/disorder in the system during the reaction. The change is positive when the products are more disordered than the starting material, negative when they are more ordered. b. Completely describe the changes (increase, decrease, why) in enthalpy and entropy that occur as one type of oil is mixed with another type of oil. Do they form a solution? Explain. First we need to separate the molecules of oil from each other. Because these are non- polar molecules, there are few strong attractive forces between them and so there is little change in enthalpy here. When we mix the molecules of the two types of oil, we make few bonds since there are few strong attractive forces between them and again there is little change in enthalpy. However, the solution is far more disordered than the two oils separately so the entropy change is positive. Thus the energy change is negative and the solution is favored. 2. (12 pts) Compare and contrast the structures of a micelle and a vesicle (liposome). A well labeled picture is worth a thousand words. In a micelle, the non-polar tails of the lipid molecules all point to the center of the sphere, out of contact with water. The polar head groups all point out, creating a polar surface in contact with water. It is tightly packed, with little room inside.
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This note was uploaded on 08/01/2008 for the course MCB 11 taught by Professor Alper during the Spring '06 term at University of California, Berkeley.

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xm-1key - MCB 11 Spring 2006 Midterm Examination I- Key M....

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