Hello, please view question and attachment below. i have some questions on the s

Question

Hello, please view question and attachment below. i have some questions on the solution itself noted with the arrows on the image. i am a little confused on some of the values. there are a total of 8 arrows but should be simple questions for those of you who are experts at thermodynamics. Please be as thorough when it comes to as to why these formulas were used. thanks for your help! Here is the question and image.

Nitrogen in a piston-cylinder assembly undergoes a polytropic expansion process. Initially, nitrogen is at 125 C and 144 kPa. Then it is expanded to a state of 102 kPa and 90 C.Determine the heat transfer and work for the process considering no change in Kinetic or Potential energy.

Explanation / Answer

1)...PV=mRT

here.m=mass,which is taken to be 1 kg(assume),because R=.297=8.314(UNIVERSAL GAS CONSTANT)/28(MOLECULAR WT OF NITROGEN),If PV =nRT,then n=1 mole and R=8.314

2)process is polytropic

for polytropic process,P1*V1Y=P2*V2Y

3) VALUE OF Y=1.3 FOR NITROGEN

4)POLYTROPIC WORKDONE=W=(P1*V1=P2*V2)/(Y-1)

5)for ideal gas and any process

or

any substance and costant pressure

this formula used.Q=m*CP*dT

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