If a system is left to change spontaneously, in what state will it end?
A the same state in which it began
B the state with the lowest possible energy consistent with the state of maximum disorder
C the state with the maximum disorder
D the state with lowest possible energy
The correct answer and explanation is:
The correct answer is D: the state with the lowest possible energy.
In any system, when left to change spontaneously, it will naturally move towards a state of equilibrium. This state is typically the one where the energy is minimized, as systems tend to move toward conditions that are energetically favorable. This principle aligns with the second law of thermodynamics, which states that in an isolated system, entropy (a measure of disorder) tends to increase. While increasing entropy implies a greater level of disorder, the system will achieve a balance between energy minimization and maximum entropy.
For example, consider a chemical reaction. The system will tend to shift towards a configuration where the total energy is as low as possible, and the system reaches its lowest potential energy. In a physical context, this could be when a gas expands to fill a container evenly, or when a solid melts into a liquid, because the process allows the system to reach a more stable (lower energy) state.
However, the idea of entropy, or disorder, does not necessarily mean that the system becomes completely disordered. It simply refers to the number of possible microstates the system can occupy. A system that is in the state of minimum energy may also exhibit a high level of disorder (maximum entropy), but the key point is that this configuration minimizes the energy, balancing it with the entropy.
In summary, a spontaneously changing system will generally reach the state with the lowest possible energy because nature favors stability, and stability often corresponds to energy minimization.