Air contained in a piston-cylinder assembly, initially at 2 bar, 200 K, and a volume of 1 L, undergoes a process to a final state where the pressure is 7.5 bar and the volume Is 2 L. During the process, the pressure-volume relatlonshlp Is lInean Assuming the ideal gas model for the alr, determine the work and heat transfer, each In kJ

Respuesta :

Answer:

Work transfer W =0.475 kJ

Heat transfer Q=3.68 KJ

Explanation:

At initial condition:

[tex]P_1=2 bar,T_1=200 K,V_1=1 L[/tex]

At final condition:

[tex]P_2=7.5 bar,V_2=2 L[/tex]

Given that pressure -volume follows linear relationship and we know that work for closed system if given as

 [tex]w=\int Pdv[/tex]

It means that are of P-v diagram will us work in that process.So we will find the are of  P-v diagram.

Now from P-v diagram

Area =[tex]\dfrac{1}{2}(P_1+P_2)(V_2-V_1)[/tex]

       =[tex]\dfrac{1}{2}(2+7.5)\times 10^{2}(2-1)\times 10^{-3}[/tex]

        =0.475 KJ

So Work transfer W =0.475 kJ

If we assume that air is ideal gas   PV=mRT

[tex]\dfrac{P_1V_1}{T_1}=\dfrac{P_2V_2}{T_2}[/tex]

[tex]\dfrac{2\times 1}{200}=\dfrac{7.5\times 2}{T_2}[/tex]

  [tex]T_2=1500 k[/tex]

From first law of thermodynamics

[tex]Q=U_2-U_1+W[/tex]       (For ideal gas U=[tex]mC_v(T_2-T_1)[/tex])

For mass [tex]P_1V_1=mRT_1[/tex]

[tex]Q=m\times 0.71(T_2-T_1)+W[/tex]

[tex]Q=3.48\times 10^{-3}\times 0.71(1500-200)+0.475[/tex]

So heat transfer Q=3.68 KJ

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