The first law of thermodynamics (which states that energy is conserved) does not specify the direction in which thermodynamic processes in nature can spontaneously occur. For example, imagine an object initially at rest suddenly taking off along a rough horizontal surface and speeding up (gaining kinetic energy) while cooling down (losing thermal energy). Although such a process would not violate conservation of energy, it is, of course, impossible and could never take place spontaneously.
The second law of thermodynamics dictates which processes in nature may occur spontaneously and which ones may not. The second law can be stated in many ways, one of which uses the concept of entropy.
a. An object at 20oC absorbs 25.0 J of heat. What is the change in entropy ΔS of the object? Express your answer numerically in joules per kelvin.
b. An object at 500 K dissipates 25.0 kJ of heat into the surroundings. What is the change in entropy ΔS of the object? Assume that the temperature of the object does not change appreciably in the process. Express your answer numerically in joules per kelvin.
c. An object at 400 K absorbs 25.0 kJ of heat from the surroundings. What is the change in entropy ΔS of the object? Assume that the temperature of the object does not change appreciably in the process. Express your answer numerically in joules per kelvin.
d. Two objects form a closed system. One object, which is at 400 K, absorbs 25.0 kJ of heat from the other object,which is at 500 K. What is the net change in entropy ΔSsys of the system? Assume that the temperatures of the objects do not change appreciably in the process. Express your answer numerically in joules per kelvin.