Midterm 2 - Study Guide

Midterm 2 - Study Guide - CHEM 124 MIDTERM 2 STUDY GUIDE...

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CHEM 124 MIDTERM 2: STUDY GUIDE Chem 124-11 Winter 2009 Chapter 20 Summary: a. for any process, chemical reactions included, one direction is spontaneous and the other is non-spontaneous b. While many exothermic reactions are spontaneous, H alone cannot predict spontaneity, i.e. ice melting above 0 ° C. c. Matter and energy tend to more disordered states or better said, to disperse they system’s energy as much as possible d. Quantum state: a total picture of an atom or molecule’s energy distribution through translational, electronic, rotational, and vibrational modes e. Microstate: a picture of every molecule in the system quantum state at any given instant; for a mol of substance at 298 K this is a staggering number: 10 Avogadro’s number f. Greater number of microstates available for a system, the more favorable it is g. A new thermodynamic variable can be defined to describe this “disorder”: entropy(S); and this can be related to the number of microstates by: S= klnW where k= 1.38 x 10 -23 J/K and W is the number of microstates (or extent to which energy of a system is dispersed) h. entropy can also be defined in terms of heat and temp: S= q rev /T Entropy change can often be described qualitatively: 1. if a pure liquid or solution forms from a solid, i.e. dissolution 2. gas formation from liquid or solid, i.e. vaporization 3. number of moles of gaseous species changes increases in the course of chemical reaction 4. temperature of a substance increases 5.
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Midterm 2 - Study Guide - CHEM 124 MIDTERM 2 STUDY GUIDE...

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