A piston-cylinder device contains 1.329 kg of nitrogen gas at 120 kPa and 27 degree C. The gas is now compressed slowly in a polytropic process during which PV^1.49 = constant. The process ends when the volume is reduced by one-half. Determine the entropy change of nitrogen during this process.

Respuesta :

Answer:-0.4199 J/k

Explanation:

Given data

mass of nitrogen(m)=1.329 Kg

Initial pressure[tex]\left ( P_1\right )[/tex]=120KPa

Initial temperature[tex]\left ( T_1\right )=27\degree \approx[/tex] 300k

Final volume is half of initial

R=particular gas constant

Therefore initial volume of gas is given by

PV=mRT

V=0.986\times 10^{-3}

Using [tex]PV^{1.49}[/tex]=constant

[tex]P_{1}V^{1.49}[/tex]=[tex]P_2\left (\frac{V}{2}\right )[/tex]

[tex]P_2[/tex]=337.066KPa

[tex]V_2[/tex]=[tex]0.493\times 10^{-3} m^{3}[/tex]

and entropy is given by

[tex]\Delta s[/tex]=[tex]C_v \ln \left (\frac{P_2}{P_1}\right )[/tex]+[tex]C_p \ln \left (\frac{V_2}{V_1}\right )[/tex]

Where, [tex]C_v[/tex]=[tex]\frac{R}{\gamma-1}[/tex]=0.6059

[tex]C_p[/tex]=[tex]\frac{\gamma R}{\gamma -1}[/tex]=0.9027

Substituting values we get

[tex]\Delta s[/tex]=[tex]0.6059\times\ln \left (\frac{337.066}{120}\right )[/tex]+[tex]0.9027 \ln \left (\frac{1}{2}\right )[/tex]

[tex]\Delta s[/tex]=-0.4199 J/k