Seeking a Criterion for Spontaneity

To understand why certain processes are spontaneous, we need to consider more closely the ways in which the state of a system can change. Recall from Section 5.2 that quantities such as temperature, internal energy, and enthalpy are state functions., properties that define a state and do not depend on how we reach that state. The heat transferred between a system and its surroundings, q, and the work done by or on the sjrstem, w, are not state functions—their values depend on the specific path taken between states. One key to imderstanding spontaneity is understanding differences in the paths between states. 

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