Thermodynamics -- first and second law concepts

Any Help

1. 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?
2. 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???

Last edited:
Related Introductory Physics Homework Help News on Phys.org

Chestermiller

Mentor
Calculate the entropy changes for the reservoirs in cases 3 and 4.

Any Help

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)

"Thermodynamics -- first and second law concepts"

Physics Forums Values

We Value Quality
• Topics based on mainstream science
• Proper English grammar and spelling
We Value Civility
• Positive and compassionate attitudes
• Patience while debating
We Value Productivity
• Disciplined to remain on-topic
• Recognition of own weaknesses
• Solo and co-op problem solving