# Thermodynamics- Nitrogen

1. 0.005 kg of nitrogen gas (N_2 – molecular weight 0.028 kg mol-1) are heated at
constant volume (V = 3.5 x 10^-3 m^3) resulting in a pressure increase from an initial
value pi = 1.2 x 10^5 Pa to a final value pf = 1.8 x 10^5 Pa. Answer the following
questions:

(a).What are the initial and final temperatures of the gas?

(b). What is the change in the internal energy of the gas?

(c). What is the work done by the gas?

(d). What is the heat flow into or out of the gas during the process?

(e). What is the change in entropy of the gas?

Hi, I am having trouble getting started on the above question could somebody please help me?

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## Answers and Replies

Mapes
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Do you know any equations relating pressure, temperature, and volume for a gas?

I seem to always have the same problem with this type of question. I know formulas for ideal gasses and think I could answer the question for an ideal gas but I am not told that the gas is ideal in the question. How do I know when I can assume it is ideal?

Mapes
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Check if the http://en.wikipedia.org/wiki/Compressibility_factor" [Broken] is sufficiently close to 1.

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When it says molar volume do you just find that by dividing the volume by the number of moles?

Mapes
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When it says molar volume do you just find that by dividing the volume by the number of moles?

Yes.

How close to 1 should I take to be sufficiently close? (I really prefer them questions which say assume it behaves like an ideal gas).

Mapes
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What did it end up being?

I couldn' t do it as I do not know the temperature of the gas. (Though thanks for the suggestion it will no doubt be useful in
other questions).

Should I just assume the gas is ideal anyway?

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Mapes
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The standard approach is to assume ideality, make the calculations, and then check the assumption.

So if something similar to this comes up in my exam (this was a past exam question) would you reccommend I just assume the gas is ideal?

Mapes
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Yes.