Chapter_19[1]

# Chapter_19[1] - Thermodynamics Describes how energy is...

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Chemical Thermodynamics   1 Thermodynamics Describes how energy is transferred or converted in chemical processes Energy conservation: the 1 st law – keeps track of energy transfer E = q + w E = total energy of a system q = heat flow w = work 2 nd law – tells conditions needed for a change to be spontaneous Entropy (S) new state function Indicates the direction of a spontaneous change Spontaneity Spontaneous process = change in system occurs without impetus Nonspontaneous process = change will not occur without doing something to make it happen q > 0 when heat flows into system q < 0 when heat flows out of system w > 0 when work is done on system w < 0 when work is done by system

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Chemical Thermodynamics   2 Difference between work and heat Heat Energy transferred into random motion Work Energy transferred into orderly motion
Chemical Thermodynamics   3 nd law Universal observation that some things occur spontaneously Ball rolls downhill Tennis balls stop moving Beakers break What do spontaneous events have in common? Energy becomes randomized 2 nd law: Energy will spontaneously move toward a more random distribution NOTE a nonspontaneous change can happen if the system is changed. (a ball will roll uphill if it is pushed)

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Chemical Thermodynamics   4 Entropy (S) Measure of how randomly energy is distributed S is larger when energy is more randomly distributed An increase in entropy is often associated with disorder E.g. ice cube contains “ordered” molecules become disordered when melts Entropy depends upon both the system and the surroundings System = region of interest (e.g. ice cube) Surroundings = everything else (e.g. water, glass, table, etc…) S tot = S sys + S sur ice 0 o C water 20 o C spontaneous Energy is not randomly distributed Energy is randomly distributed Entropy increases
Chemical Thermodynamics   5 Effect of S sys & S sur Water becomes more ordered Salt becomes less ordered

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Chapter_19[1] - Thermodynamics Describes how energy is...

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