ATH 101: Efficiency of Isobaric Expansion for Monatomic and Diatomic Gases

[pride443]

In a heat engine we ultimately care about the efficiency of the entire cycle. That is,
what percentage of the heat which flows into your system is converted to work. However,
you could certainly ask that same question for an individual step in a cycle. Specifically,
determine the efficiency of an isobaric process which takes a system from a volume V to a
volume αV where α > 1. You will not need to know the actual value of α. In the end, it
will cancel out of all expressions.
a: Do this calculation if the gas is monatomic.
b: Do this calculation if the gas is diatomic.

I'm stuck on trying to incorporate variables beyond

E=(3/2)(8.134)T-a/V

 

[Andrew Mason]

In a heat engine we ultimately care about the efficiency of the entire cycle. That is,
what percentage of the heat which flows into your system is converted to work. However,
you could certainly ask that same question for an individual step in a cycle. Specifically,
determine the efficiency of an isobaric process which takes a system from a volume V to a
volume αV where α > 1. You will not need to know the actual value of α. In the end, it
will cancel out of all expressions.
a: Do this calculation if the gas is monatomic.
b: Do this calculation if the gas is diatomic.

I'm stuck on trying to incorporate variables beyond

E=(3/2)(8.134)T-a/V

Start with the definition of efficiency:

η = output/input = W/Qin

What is Qin for an isobaric expansion from V to αV? What is W? (hint: express each in terms of ΔT)

AM