The Nature of Spontaneous Processes

In preparation for setting up the second law of thermodynamics and stating precisely the criteria for spontaneity, we will examine several familiar examples of spontaneous processes and describe their features in general terms. A spontaneous change is one that can occur by itself without outside intervention, once conditions have been established for its initiation. The change may be fast or slow, and we may have to wait a significant period to determine whether it does occur. 

One of the most striking features of spontaneous change is that it follows a specific direction when starting from a particular initial condition. A quite 

FIGURE 13.1 A bullet hitting a steel plate at a speed of 1600 ft/sec melts as its kinetic energy is converted to heat, and metal droplets spray in all directions. These three photographs make sense only in the order shown the reverse process is unmistakably implausible. 

Spontaneous processes familiar in chemical laboratories also follow specific directions  

We measure heat flowing from a hot body to a cold one when they are brought into thermal contact, but we never detect heat flowing spontaneously in the opposite direction. 

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This chapter begins with a discussion of the three laws of thermodynamics and the nature of spontaneous processes. (18.1 and 18.2)... 

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