Carbon dioxide contained in a piston–cylinder device is compressed from 0.3 to 0.1 m3. During the process, the pressure and volume are related by P = aV–2, where a = 6.5 kPa·m6.
Calculate the work done on carbon dioxide during this process.

Respuesta :

Answer:

[tex] W = -6.5 Kpa m^6 (\frac{1}{0.1 m^3}- \frac{1}{0.3 m^3})= -6.5 Kpa m^6 (6.66 m^-3) =-43.33 Kpa m^3 = -43.33 KJ[/tex]

Explanation:

For this case we know the following info :

[tex] V_i = 0.3 m^3 [/tex] represent the initial volume

[tex] V_f = 0.1 m^3[/tex] represent the final volume

We know that the pressure and volume are related with the following expression:

[tex] P = aV^{-2}= \frac{a}{V^2}[/tex]

Where a is a constant given [tex]a = 6.5 Kpa m^6[/tex]

And we need to calculate the work associated to this process.

We have a compression, and by definition the work is defined with the following general expression:

[tex] W = \int_{V_i}^{V_f} P dV[/tex]

If we replace the expression for P we got:

[tex] W = \int_{V_i}^{V_f} a V^{-2} dV[/tex]

If we integrate we got:

[tex] W = -a (\frac{1}{V}) \Big|_{V_i}^{V_f}[/tex]

Using the fundamental theorem of calculus we have:

[tex] W = -a (\frac{1}{V_f} -\frac{1}{V_i})[/tex]

And replacing the values we got:

[tex] W = -6.5 Kpa m^6 (\frac{1}{0.1 m^3}- \frac{1}{0.3 m^3})= -6.5 Kpa m^6 (6.66 m^-3) =-43.33 Kpa m^3 = -43.33 KJ[/tex]

The work done on carbon dioxide during this process is; -43.33 kJ

What is work done?

For the Polytropic process, we are given the relationship between pressure and volume as; P = aV⁻² = a/V²

To get the work done, we have to integrate the pressure to get;

W = ∫P = ∫a/V² = -a/V

Work done from 0.3 m³ to 0.1 m³, we have;

W = -6.5(¹/₀.₁ - ¹/₀.₃)

W = -43.33 kPam³ = -43.33 kJ

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