What Is the Value of n in the Gas Law Equation for a Given Process?

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The discussion revolves around solving a gas law equation for a closed system with given pressures and volumes. The main question is determining the value of n in the equation pV^n=constant, where unit conversions are not necessary as the units will cancel out. Participants clarify that specific volume can be calculated using mass, but there is confusion regarding whether the 2 lb refers to mass or weight, as the text does not specify. Additionally, there is a request for clarification on how to sketch the process on pressure-volume coordinates, emphasizing the need to plot intermediate points. Overall, the conversation highlights the importance of understanding units and graphing in thermodynamic processes.
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Homework Statement


A closed system consisting of 2 lb of a gas undergoes a process in which pV^n=constant. For: p1=20 lb/in^2 , V1=10 ft^3 and p2=100lb/in^2 V2=2.9 ft^3

(a)What is n ?

(b)What is the specific volume at states 1 and 2 in ft^3/lb?

(c)Sketch the process on pressure-volume coordinates


For (a), I don't need to convert the units all to feet or all to inches right? i can just say p1V1^n=p2V2^n correct?

(b) Is just a matter of find the mass m=Weight/g

(c) Is confusing me? Is this just a graph? With p on the horizontal axis and V on the vertical?


Thanks!
 
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Okay, I got (a)...the units cancel anyway.

But for (b) I cannot tell if they are giving me 2lb as a mass or as a weight. It's a thermodynamics book, so I don't know what the convention is? they did not specify lbf (force) or lbm (mass)
 
Saladsamurai said:

Homework Statement


A closed system consisting of 2 lb of a gas undergoes a process in which pV^n=constant. For: p1=20 lb/in^2 , V1=10 ft^3 and p2=100lb/in^2 V2=2.9 ft^3

(a)What is n ?

(b)What is the specific volume at states 1 and 2 in ft^3/lb?

(c)Sketch the process on pressure-volume coordinates


For (a), I don't need to convert the units all to feet or all to inches right? i can just say p1V1^n=p2V2^n correct?
Correct.

P_1V_1^n = 5P_1(.29V_1)^n


(b) Is just a matter of find the mass m=Weight/g
Correct

(c) Is confusing me? Is this just a graph? With p on the horizontal axis and V on the vertical?
You have to plot points in between the end points as well.

AM
 
Saladsamurai said:
Okay, I got (a)...the units cancel anyway.

But for (b) I cannot tell if they are giving me 2lb as a mass or as a weight. It's a thermodynamics book, so I don't know what the convention is? they did not specify lbf (force) or lbm (mass)
Are the units of pressure Force/area or mass/area?

AM
 

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