- #1
yaylee
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Homework Statement
Which of the following statements about entropy and heat engines are true? (There is more than one right answer!)
1)The entropy of the universe can never decrease
2) The COP (coefficient of performance) of a refrigerator can never be greater than 1
3) All Carnot engines are reversible
4) A refrigerator lowers the entropy of the volume inside
5) If the temperature of the cold reservoir increases with the temperature of the hot reservoir unchanged, the efficiency of a Carnot engine will increase
6) Any process that includes adding heat to an ideal gas will increase the entropy of the gas
7)It is impossible have a net transfer of heat from a cold reservoir to a warm reservoir
8) All Carnot engines are more efficient than all real engines
9) All heat engines operating between the same temperatures have the same efficiency
10)Adiabatic expansion will lower the temperature of a gas
11) The entropy of a system can never decrease
12) The efficiency of a Carnot engine can never be 1
Homework Equations
Entropy = dQ/T
efficiency of Carnot Engine = 1 - (Tc/Th), where Tc = Temp of cold reservoir, Th = hot.
Coefficient of Performance C.O.P = Qc/W, where Qc = heat absorbed into cold reservoir
Work done in ANY cycle, W = Qh - Qc.
The Attempt at a Solution
Note: I bolded the correct answer, with explanation below the correct statement!
1)The entropy of the universe can never decrease
By definition, entropy will be equal to 0 in a Carnot cycle, greater than 0 in a real cycle..
2) The COP (coefficient of performance) of a refrigerator can never be greater than 1
3) All Carnot engines are reversible
By definition, Carnot engines are quasi-static, reversible processes.
4) A refrigerator lowers the entropy of the volume inside
Decreasing entropy is analagous to saying you are "removing heat" from the refrigerator.
5) If the temperature of the cold reservoir increases with the temperature of the hot reservoir unchanged, the efficiency of a Carnot engine will increase
e = 1 - Tc/Th. Increasing Tc will decrease e.
6) Any process that includes adding heat to an ideal gas will increase the entropy of the gas
By definition, dS = +dQ/T, so dS is positive.
7)It is impossible have a net transfer of heat from a cold reservoir to a warm reservoir
8) All Carnot engines are more efficient than all real engines
Simple definition.
9) All heat engines operating between the same temperatures have the same efficiency
10)Adiabatic expansion will lower the temperature of a gas
11) The entropy of a system can never decrease
Simple definition.
12) The efficiency of a Carnot engine can never be 1
At absolute zero, this will be true.
Pls point out where I may have missed a true statement, or marked a true statement which is actually false. Many thanks in advance for your help! Infinite appreciation !