ACS Physical Chemistry: Thermochemistry 2025 – 400 Free Practice Questions to Pass the Exam

Non-spontaneous processes are fundamentally characterized by their requirement for an input of energy or work to proceed. This means that they do not happen on their own under the given conditions and instead rely on external factors to drive them. For example, if a chemical reaction is non-spontaneous at a certain temperature, it will need an external energy source, such as heat or electrical energy, to occur.

In contrast, spontaneous processes happen naturally and do not require continuous input of energy; they can release energy as a result of their progression. The option regarding the production of work is misleading because non-spontaneous processes do not yield energy or work; instead, they need energy input to transform the system into a more favorable state.

Irreversibility is a characteristic that can apply to many spontaneous processes, especially in terms of thermodynamic processes involving entropy. However, non-spontaneity primarily revolves around the need for work or energy to initiate the process, making the requirement for work the defining aspect.