A rigid tank contains an ideal gas at 40°C that is being stirred by a paddle wheel. The paddle wheel does 240 kJ of work on the ideal gas. It is observed that the temperature of the ideal gas remains constant during this process as a result of heat transfer between the system and the surroundings at 30°C. Determine the entropy change of the ideal gas.

Respuesta :

To solve the problem it is necessary to consider the concepts and formulas related to the change of ideal gas entropy.

By definition the entropy change would be defined as

[tex]\Delta S = C_p ln(\frac{T_2}{T_1})-Rln(\frac{P_2}{P_1})[/tex]

Using the Boyle equation we have

[tex]\Delta S = C_p ln(\frac{T_2}{T_1})-Rln(\frac{v_1T_2}{v_2T_1})[/tex]

Where,

[tex]C_p[/tex] = Specific heat at constant pressure

[tex]T_1[/tex]= Initial temperature of gas

[tex]T_2[/tex]= Final temprature of gas

R = Universal gas constant

[tex]v_1[/tex]= Initial specific Volume of gas

[tex]v_2[/tex]= Final specific volume of gas

According to the statement, it is an isothermal process and the tank is therefore rigid

[tex]T_1 = T_2, v_2=v_1[/tex]

The equation would turn out as

[tex]\Delta S = C_p ln1-ln1[/tex]

Therefore the entropy change of the ideal gas is 0

Into the surroundings we have that

[tex]\Delta S = \frac{Q}{T}[/tex]

Where,

Q = Heat Exchange

T = Temperature in the surrounding

Replacing with our values we have that

[tex]\Delta S = \frac{230kJ}{(30+273)K}[/tex]

[tex]\Delta S = 0.76 kJ/K[/tex]

Therefore the increase of entropy into the surroundings is 0.76kJ/K