Nitrogen at 100 kPa and 25oC in a rigid vessel is heated until its pressure is 300 kPa. Calculate (a) the work done and (b) the heat transferred during this process, in kJ/kg. [use the room temperature specific heat for nitrogen] [for nitrogen Tcr=126.2 K, Pcr=3.39 MPa]

Respuesta :

Answer:

A. The work done during the process is W = 0

B. The value of heat transfer during the process Q = 442.83 [tex]\frac{KJ}{kg}[/tex]

Explanation:

Given Data

Initial pressure [tex]P_{1}[/tex] = 100 k pa

Initial temperature [tex]T_{1}[/tex] = 25 degree Celsius = 298 Kelvin

Final pressure [tex]P_{2}[/tex] = 300 k pa

Vessel is rigid so change in volume of the gas is zero. so that initial volume is equal to final volume.

[tex]V_{1}[/tex] = [tex]V_{2}[/tex] ------------- (1)

Since volume of the gas is constant so pressure of the gas is directly proportional to the temperature of the gas.

⇒ P ∝ T

⇒ [tex]\frac{P_{2} }{P_{1}}[/tex] = [tex]\frac{T_{2} }{T_{1}}[/tex]

⇒ Put all the values in the above formula we get the final temperature

⇒ [tex]T_{2}[/tex] = [tex]\frac{300}{100}[/tex] × 298

[tex]T_{2}[/tex] = 894 Kelvin

(A). Work done during the process is given by W = P × ([tex]V_{2} -V _{1}[/tex])

From equation (1), [tex]V_{1}[/tex] = [tex]V_{2}[/tex] so work done W = P × 0 = 0

⇒ W = 0

Therefore the work done during the process is zero.

Heat transfer during the process is given by the formula Q = m [tex]C_{v}[/tex] ( [tex]T_{2}[/tex] -[tex]T_{1}[/tex] )

Where m = mass of the gas = 1 kg

[tex]C_{v}[/tex] = specific heat at constant volume of nitrogen = 0.743 [tex]\frac{KJ}{kg k}[/tex]

Thus the heat transfer Q = 1 × 0.743 × ( 894- 298 )

⇒ Q = 442.83 [tex]\frac{KJ}{kg}[/tex]

Therefore the value of heat transfer during the process Q = 442.83 [tex]\frac{KJ}{kg}[/tex]