Question

For each answer, please briefly explain the reasoning behind the answer.

1. True or False: For heat pumps, wcycle, irreversible > wcycle, reversible

2. True or False: All pure substances must have S = 0 at T = 0 K.

3. True or False: The maximum theoretical efficiency of a reversible heat engine will decrease if the working substance is a real gas instead of an ideal gas.

4. A reversible process is carried out on an ideal gas NOT under constant pressure conditions. Given that for this process ΔS > 0 and ΔH = 0,

a. the system absorbs heat and expands during the process.

b. the system absorbs heat and contracts during the process.

c. the system loses heat and expands during the process.

d. the system loses heat and contracts during the process.

e. cannot be determined from the information given.

Answer 1

1) True

2)   All pure substances must have S = 0 at T = 0 K.   True

   
Standard entropies have been determined for many substances , and these values are
based on the third law of thermodynamics
The entropy of the pure substances at 0 K is zero.
as the temperature increases from 0 K entropy also increases, because as temperature
increases thermal motions increases resulting disorder increases.

3)    True The maximum theoretical efficiency of a reversible heat engine will decrease if the working substance is a real gas instead of an ideal gas.

        if working substance is ideal gas then the efficiency is one if the it is real gas the efficiency will be less than one

4)     A reversible process is carried out on an ideal gas NOT under constant pressure conditions. Given that for this process ΔS > 0 and ΔH = 0

   option a is correct     the system absorbs heat and expands during the process