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Fundamentals Of Physics
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Short Answer

An ideal gas initially at 300K is compressed at a constant pressure of 25 N/m2 from a volume of 3.0m3to a volume of 1.8 m3 . In the process, 75J is lost by the gas as heat. What are

(a) the change in internal energy of the gas and

(b) the final temperature of the gas?

  1. The internal energy change in the gas isΔEint=45 J .
  2. The temperature of the gas changes to180 K .
See the step by step solution

Step by Step Solution

Step 1: Concept

The process that takes place at constant pressure is called an isobaric process. Using the formulas for work done W in an isobaric process, and the first law of thermodynamics, we can find the change in the internal energy ΔEint of the gas. Also, by using the ideal gas law in the ratio form, we can find the final temperature T2of the gas.

1.The work done W in anisobaric process is

W=pΔV

2.The ideal gas law in ratio form is

T2=T1V2V1

3.The change in the internal energy is

ΔEint=Q-W

Step 2: Given Data

  1. The pressure .p=25 N/m2
  2. The final volume Vf=1.8 m3
  3. The initial volume .Vi=3.0 m3
  4. The initial temperature T1=300 K
  5. In the process, the energy lost by the gas as heat isQ=75 J .

Step 3: Calculations

a.The work done in anisobaricprocess is expressed as-

W=pΔV

Where p is the pressure and ΔV=(VfVi)is change in the volume

Therefore,

W=p(VfVi)=25 N/m2×(1.8 m33.0 m3)=30 J

From the first law of thermodynamics, we have-

ΔEint=QW

Where Q is the heat transferred and ΔEint is the change in the internal energy o the gas. It is given that Q amount of energy leaves the system; therefore, we can consider Q as negative. Q=75 J

ΔEint=75 J(30 J)=75 J+(30 J)=45 J

Internal energy is decreased by 45 J

b.Since the pressure is constant and the number of moles presumed are constant, the ideal gas law can be written as-

T2=T1(V2V1)=300 K×(1.8 m33.0 m3)=180  K

Step 4: Conclusion

The change in internal energy of the gas is -45Jand the final temperature of the gas is 180 K.

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