The second law of thermodynamics explains the direction in which the thermodynamic processes tend to go. That is, it limits the types of final states of the system that naturally evolve from a given initial state. The second law has many practical applications. For example, it explains the limits of efficiency for heat engines and refrigerators.
To develop a better understanding of this law, try these conceptual questions:

A. The thermodynamic processes that occur in nature .

a) convert thermal energy into mechanical energy
b) lead to a more ordered state
c) cannot be reversed
d) do not conserve energy

B. According to the second law of thermodynamics, it is impossible for .

a) heat energy to flow from a colder body to a hotter body
b) an ideal heat engine to have the efficiency of 99%
c) an ideal heat engine to have non-zero power
d) a physical process to yield more energy than what is put in

C. If the coefficient of performance of a refrigerator is 1, which the following statements is true?

a) The temperature outside equals the temperature inside of the refrigerator.
b) The rate at which heat is removed from the inside equals the rate at which heat is delivered outside.
c) The power consumed by the refrigerator equals the rate at which heat is removed from the inside.
d) The power consumed by the refrigerator equals the rate at which heat is delivered to the outside.

D. To increase the efficiency of an ideal heat engine, one must increase which of the following?

a) the amount of heat consumed per second.
b) the temperature of the cold reservoir.
c) the temperature of the hot reservoir.
d) the size of the cold reservoir.
e) the size of the hot reservoir.

E. How would you increase the coefficient of performance of an ideal refrigerator?

a) Increase the mechanical work input.
b) Decrease the outside temperature.
c) Decrease the inside temperature.
d) Increase the outside temperature.