Calculate the change in the entropies of the system and the surroundings, and the total change in entropy, when a sample of nitrogen gas of mass 14 g at 298 K and 1.00 bar doubles its volume in (a) an isothermal reversible expansion, (b) an isothermal irreversible expansion against pex = 0, and (c) an adiabatic reversible expansion.

Respuesta :

Our values are:

[tex]m=14g\\T=298K\\P=1bar[/tex]

a) For isothermal reversible expansion, We have that the change in the Internal Energy is 0, that is,

[tex]\Delta U = 0[/tex]

We can solve for the Work made in the system.

[tex]|q| = |W|= nRT ln(\frac{V_2}{V1} )[/tex]

[tex]|W| = \frac{1}{2}*8.314*298*ln(2) = 858.66J[/tex]

With work made it, this same quantity is necessary to add to the system through Heat. Then,

[tex]\Delta S_{system} = \frac{Q_{rev}}{T} = \frac{858.66}{298} = 2.88 J/K[/tex]

For Surrounding we apply the same relation,

[tex]\Delta S_{surrounding} = \frac{Q_{surrounding}}{T} = \frac{-858.66}{T} = -2.88J/K[/tex]

Therefore, [tex]\Delta S_{total} = 0[/tex]

b) For an isothermal irreversible expansion

We consider the external presion as 0, by this way, the work done is also 0.

[tex]P_{ext} = 0 \Rightarrow W=0[/tex]

Since isothermal irreversible expansion change in Internal Energy is 0, so

[tex]\Delta U = q = 0[/tex], since isothermal

Therefore

[tex]\Delta S_{surr} = 0[/tex]

How the condition are the same, for the System the entropy is the same

But [tex]\Delta S{system} = 2.88 J/K[/tex]

[tex]\Delta S_{total} = 2.88 J/K[/tex]

c) And an adiabatic reversible expansion

Since the process is Adiabatic,

[tex]q = 0[/tex]

Therefore, [tex]\Delta S_{sys} =0 \Rightarrow \Delta S_{surr} = 0[/tex]

The mass of nitrogen = 14kg

Temperature = 298 k

Pressure = 1 bar

The work in the system

0.5*8.314*298*ln2

= 858.7 Joules

Next we have to solve for the system through the heat

858.7/298

= 2.8814J/K

This is the same as the temperature that is in the surrounding. We conclude that the change in isothermal expansion = 0

b. Isothermal change in the equation = 0

This means that the process is the same as in a above.

c. Given that this is an adiabatic expansion then q = 0.

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