Advanced Placement (AP) Chemistry Practice Exam

What is the primary indication of a system's randomness or disorder?

1. Entropy

2. Enthalpy

3. Gibbs free energy

4. Oxidation state

The correct answer is: Entropy

The primary indication of a system's randomness or disorder is entropy. In thermodynamics, entropy is a measure of the number of microscopic configurations that correspond to a thermodynamic system at a given energy level. A higher entropy value indicates greater disorder and randomness within the system, meaning that the particles are more dispersed and energy distribution is more uniform. Entropy plays a crucial role in the second law of thermodynamics, which states that in an isolated system, the total entropy tends to increase over time, leading to a natural tendency towards disorder. Understanding entropy is key for predicting the direction of spontaneous processes; systems tend to move toward states of higher entropy. Other concepts like enthalpy and Gibbs free energy are important in thermodynamics as well but are not direct measures of disorder. Enthalpy relates to the total heat content of a system, while Gibbs free energy combines both enthalpy and entropy to determine the spontaneity of processes, but neither directly measures randomness. The oxidation state is a concept used to keep track of electron transfer in chemical reactions and does not pertain to disorder or randomness.