Defining Spontaneous Processes
A spontaneous process is one that occurs naturally without continuous external intervention once initiated. These processes tend to proceed in a direction that lowers the system's free energy or increases its overall entropy (disorder) in the universe. Examples include a ball rolling downhill, ice melting at room temperature, or rust forming on iron when exposed to air and moisture.
Defining Non-Spontaneous Processes
A non-spontaneous process is one that will not occur naturally and requires a continuous input of energy from an external source to proceed. These processes typically move towards a state of higher free energy or decreased entropy. Examples include charging a battery, pumping water uphill against gravity, or separating mixed gases into pure components.
The Role of Gibbs Free Energy (ΔG)
The spontaneity of a process at constant temperature and pressure is primarily determined by the change in Gibbs Free Energy (ΔG). For a spontaneous process, ΔG is negative (ΔG < 0), indicating that the system releases free energy. For a non-spontaneous process, ΔG is positive (ΔG > 0), meaning energy must be supplied to the system. If ΔG = 0, the system is at equilibrium, with no net change.
Factors Influencing Spontaneity
The Gibbs Free Energy change (ΔG) is related to enthalpy (ΔH, heat change) and entropy (ΔS, disorder) by the equation ΔG = ΔH - TΔS, where T is the absolute temperature. A process can become spontaneous or non-spontaneous depending on the magnitudes and signs of ΔH and ΔS, and the temperature. For instance, an endothermic (ΔH > 0) process might be non-spontaneous at low temperatures but become spontaneous at high temperatures if ΔS is positive.