# Physics Heat transfer question (will award BEST ANSWER)?

Physics Heat transfer question (will award BEST ANSWER)?

• A

Process A is a constant volume process. The heat transferred in such a process equals the change in internal energy of the gas.

Q = βU

Assuming ideal gas behavior the change in internal energy of the nitrogen gas is given by:

βU = nβCvββT

The molar heat capacity at constant volume for an diatomic ideal gas like nitrogen is

Cv = (5/2)βR

Hence,

Q =β(5/2)βnβRββT

From ideal gas law

nβRβT = pβV

follows for an constant volume process:

nβRββT = β(pβV) = Vββp

Hence,

Q =β(5/2)βVββp = (5/2)βVβ(p_f – p_i)

= (5/2) β 2000cmΒ³ β (1atm – 3atm)

= (5/2) β 2000mΒ³Γ10β»βΆmΒ³ β (- 2 β 1.01325Γ10β΅ Pa)

= -1013.25 J

B

Process B is a constant pressure process. The heat transferred in such a process equals the change in enthalpy of the gas.

Q = βH

Assuming ideal gas behavior the change in enthalpy of the nitrogen gas is given by:

βH = nβCpββT

The molar heat capacity at constant pressure for an diatomic ideal gas like nitrogen is

Cv = (7/2)βR

Hence,

Q =β(5/2)βnβRββT

From ideal gas law

nβRβT = pβV

follows for an constant pressure process:

nβRββT = β(pβV) = pββV

Hence,

Q =β(7/2)βpββV = (5/2)βpβ(V_f – V_i)

= (7/2) β 2atm β (3000cmΒ³ – 1000cmΒ³)

= (7/2) β 2β1.01325Γ10β΅ Pa β 2000mΒ³Γ10β»βΆmΒ³

= 1418.55 J