I need help with 2 thermodynamics questions
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I need help with 2 thermodynamics questions

[From: ] [author: ] [Date: 12-02-14] [Hit: ]
Change in internal energy is 0 because it is an isothermal process.The only thing that varies is T.If T doesnt change, neither does Eint.......
1. What is the maximum possible efficiency for a heat engine operating between heat reservoirs whose temperatures are 800 degrees C and 200 degrees C?

2. An ideal gas is compressed isothermally from 20L to 10L. During this process, 5J of work is done to compress the gas. /what is the change of internal energy for this gas?

I've tried each of them many times and cannot get the right answer (I keep getting 75% for 1 and 5J for 2. My friends don't know how to do this either! Thanks in advance.

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1. Convert degrees C to Kelvin before calculating efficiency and you'll get it right.

2. Change in internal energy is 0 because it is an isothermal process.
From kinetic theory:
Eint = f/2nRT
f is the degrees of freedom of the gas (constant)
n is the number of moles of gas molecules (constant)
R is a constant
The only thing that varies is T. If T doesn't change, neither does Eint.
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