Thermodynamics -- first and second law concepts

AI Thread Summary
The discussion revolves around an inventor's claim of four engines operating between constant-temperature reservoirs at 400 K and 300 K. Each engine's performance data is analyzed to determine violations of the first and second laws of thermodynamics. It is established that engines one and two violate the first law, as their heat input is less than the sum of work output and heat rejected. For engines three and four, participants suggest calculating entropy changes to assess potential violations of the second law. The efficiency of the engines is also discussed, emphasizing that it should not exceed 40% for a Carnot engine.
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Homework Statement


An inventor claims to have invented four engines, each of which operates between constant-temperature reservoirs at 400 and 300 K. Data on each engine, per cycle of operation, can be found in the table below. Of the first and second laws of thermodynamics, which (if either) does each engine violate?
Engine |||||||||| 1 ||||||||||| 2 |||||||||| 3 |||||||||| 4
QH |||||||||||| 200J ||||| 500J||||||| 600J ||||| 100J
QL||||||||||||| -175J||||| -200J|||||| -200J|||||| -90J
W |||||||||||||||40J ||||||||400J ||||||||400J|||||||10J
Of the first and second laws of thermodynamics, which (if either) does each engine violate?

Homework Equations


should i use the efficiency rule? I know that first law says that the total energy of an isolated system is constant; energy can be transformed from one form to another, but cannot be created or destroyed. then Qh=|Qc|+W then one and two violates first law since in both Qh<|Qc|+W But how can i show that three and four violates the second law?
 
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Calculate the entropy changes for the reservoirs in cases 3 and 4.
 
Chestermiller said:
Calculate the entropy changes for the reservoirs in cases 3 and 4.
Yeah, Thanks I didn't pay attention to that at the beginning
also we could relate it to the efficiency for which it must not be greater than 40% (carnot engine)
 
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