Spontaneous process

Definition

A spontaneous process is a physical or chemical change that occurs without the need for external energy input. These processes tend to happen naturally and result in an increase in the overall entropy of the system and its surroundings, reflecting the tendency of systems to evolve toward a state of greater disorder.

5 Must Know Facts For Your Next Test

1. Spontaneous processes can be endothermic or exothermic; they are characterized by their ability to proceed without external energy, but they can either absorb or release heat.
2. The total entropy of an isolated system will always increase during a spontaneous process, aligning with the second law of thermodynamics.
3. Even if a process is spontaneous, it can occur at a very slow rate, as seen in reactions like rusting or the melting of ice at room temperature.
4. A spontaneous process is often indicated by a negative change in Gibbs free energy (ΔG < 0), suggesting that the products are more stable than the reactants.
5. Many spontaneous processes are driven by factors like temperature, pressure, and concentration changes, which influence how quickly or slowly these changes occur.

Review Questions

• How does the concept of entropy relate to spontaneous processes?
  • Entropy is central to understanding spontaneous processes because these processes typically lead to an increase in entropy. The second law of thermodynamics states that the total entropy of an isolated system will always increase over time. This means that spontaneous processes move towards states of greater disorder, which is represented by higher entropy levels. Therefore, when assessing whether a process is spontaneous, one must consider its impact on the entropy of the system and its surroundings.
• What are some examples of spontaneous and non-spontaneous processes, and how do their energy requirements differ?
  • Spontaneous processes include the melting of ice at room temperature and the combustion of gasoline, both occurring naturally without external energy input. In contrast, non-spontaneous processes like electrolysis require an external energy source to occur. The difference lies in their energy dynamics; spontaneous processes release energy or increase entropy naturally, while non-spontaneous processes must be driven by added energy to overcome thermodynamic barriers.
• Evaluate the role of temperature in influencing whether a process is spontaneous or non-spontaneous.
  • Temperature plays a crucial role in determining if a process is spontaneous. For example, some reactions may only be spontaneous at high temperatures due to an increase in entropy that outweighs enthalpy changes. Conversely, certain reactions may be spontaneous at low temperatures but become non-spontaneous as temperature increases. The Gibbs free energy equation ($$ ext{ΔG} = ext{ΔH} - T ext{ΔS} $$) illustrates this relationship: when temperature rises, the influence of entropy (ΔS) becomes more significant in determining spontaneity, potentially shifting a process from being spontaneous to non-spontaneous or vice versa.

Related terms

Entropy:

A measure of the degree of disorder or randomness in a system, which tends to increase in spontaneous processes according to the second law of thermodynamics.

Thermodynamic Equilibrium: A state in which a system's macroscopic properties remain constant over time, indicating that no net changes are occurring, often as a result of spontaneous processes reaching balance.

Non-spontaneous Process: A process that does not occur naturally and requires an input of energy to proceed, such as the electrolysis of water.