Lecture 7, 1-23-08 Spontaneous processes

Lecture 7, 1-23-08 Spontaneous processes - SPONTANEITY...

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¾ Spontaneous process – one that proceeds on its own without any external influence ¾ The reverse of any spontaneous process is always nonspontaneous ¾ From a thermodynamic standpoint, spontaneity is not related to speed -: a spontaneous reaction may occur slowly SPONTANEITY
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Ice melting at room temperature Formation of water from O 2 (g) and H 2 (g): Expansion of gas into an evacuated space 2H 2 (g) + O 2 (g) 2H 2 O(g) Pt cat Examples of Spontaneous Processes
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A Spontaneous Process: Heat always flows from high temperature to low temperature
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Steady heat transfer without work transfer happens frequently Q Q Hot T Cold T
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Observation: Non-spontaneous process Q Q Hot T Cold T Heat will Heat will not not flow from a cooler to flow from a cooler to a hotter temperature spontaneously. a hotter temperature spontaneously. Never happens unless work is done
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Observation: non-spontaneous process A cyclic heat engine A cyclic heat engine cannot cannot operate with operate with one heat reservoir. one heat reservoir. Work During Cycle, W Cycle Q 1 Heat Reservoir Note that if Q 1 = W Cycle , then a perpetual machine is possible! T hot T cold
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There is a natural direction of all There is a natural direction of all processes towards a state of processes towards a state of lower lower potential to do work. potential to do work. There is tendency in all There is tendency in all processes and cyclic devices to processes and cyclic devices to produce produce unrecoverable unrecoverable energy energy in either doing or consuming in either doing or consuming work. work.
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Lecture 7, 1-23-08 Spontaneous processes - SPONTANEITY...

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