The pressure of gas changes linearly with volume from 10 kPa, 200 cc to 50 kPa, 50 cc.
(a) Calculate the work done by the gas.
(b) If no heat is supplied or extracted from the gas, what is the change in the internal energy of the gas?
Given
Initial pressure P1=10kPa=10×103Pa
Final pressure P2=50kPa=50×103Pa
Initial volume V1=200cc=200×10-6m3
Final volume V2=50cc= 50×10-6m3
a) We know that,
Work done = force ×displacement
Volume = area ×displacement
Therefore,
Work done=pressure ×volume
Let change in the volume of system = ΔV = V2-V1
Pressure =P
Thus, work done by the gas
ΔW=PΔV
Here we have given two values of pressure. So, we will take the average value of pressure
Average pressure P
Therefore, ΔW = 30×103× (50-200)×10-6
ΔW= -4.5J
Work done by the gas is -4.5J.
b) Given that no heat is supplied or extracted from the gas.
From first law of thermodynamics, we know that,
ΔQ=ΔU+ΔW
Where ΔQ=heat supplied to the system
ΔU=change in internal energy
ΔW=work done by the system
Since ΔQ=0
Therefore ΔU = -ΔW = -(-4.5) J=4.5J
∴ the change in internal energy of the gas is 4.5J.