- #1
<---
- 52
- 0
Homework Statement
A Carnot engine operates on 1 Kg of CH4, which we shall consider an ideal gas. Take [tex]\gamma[/tex]=1.35. The ratio of max to min volume is 4 and the cycle efficency is 25%. Find the entropy increase during the isothermal expansion.
[Classical and Statistical Thermodynamics, Ashley H. Carter, pg.104]
Homework Equations
dU = TdS-PdV
The Attempt at a Solution
Ideal gas, isothermal expansion,[tex]\Rightarrow[/tex] dU = 0
[tex]\Rightarrow[/tex] dS=[tex]\frac{P}{T}[/tex]dV=nR[tex]\frac{dV}{V}[/tex]
[tex]\Rightarrow[/tex] [tex]\Delta[/tex]S=R(62.5)ln(4)=720J/K
The correct answer is 294J/K
I know my problem has to be with the number of moles, probably accounting for the efficiency. working backwards I see there should be 25.5 moles of methane for n.
How do I account for the efficiency and get this answer?