Question

Pressurized air, which is modeled as an ideal gas with a gas constant of R = 287 J/kg-K, is contained in a rigid gas cylinder. The constant-volume specific heat of air, Cv,air=718 J/kg-K. The initial state (state1) of the air is T1=300 K, P1=5x105 Pa, V1=1 m3 The air container is moved to a very cold area and its temperature is decreased to T2=250 K. Assume the air container is rigid and there is no leakage of air. Calculate

1) the amount of heat transfer the air experienced during the change of state 1 to 2.

2) change of entropy of air during the change of state 1 to 2. Is entropy increased or decreased? If decreased, why?

3) the amount of entropy generation during the process 1 to 2. Assume the surrounding air (T0=250 K) is an ideal heat reservoir. (Tip: Define the system boundary such that it is placed in the surrounding air. Then, the boundary temperature is a constant at T0=250 K and the entropy transfer from the pressurized air to the surrounding air can be simply calculated as Q1-2/T0.)

Answer 1

Whenever the Temperature of the system decreases means the energy processed by the atoms or molecules release thus they reduce their motion due to lack of energy. I e leads to the reduction in the randomness of the atoms and molecules. Since entropy means that the degree of randomness since randomness decreases resulting entropy decreases