JEE Main & Advanced Chemistry Thermodynamics / रासायनिक उष्मागतिकी Spontaneous And Non-Spontaneous Processes

A process which can take place by itself under the given set of conditions once it has been initiated if necessary, is said to be a spontaneous process. In other words, a spontaneous process is a process that can occur without work being done on it. The spontaneous processes are also called feasible or probable processes.

On the other hand, the processes which are forbidden and are made to take place only by supplying energy continuously from outside the system are called non-spontaneous processes. In other words, non spontaneous processes can be brought about by doing work.

 Examples of Spontaneous and Non-spontaneous processes

 (1) The diffusion of the solute from a concentrated solution to a dilute solution occurs when these are brought into contact is spontaneous process.

 (2) Mixing of different gases is spontaneous process.

 (3) Heat flows from a hot reservoir to a cold reservoir is spontaneous process.

 (4) Electricity flows from high potential to low potential is spontaneous process.

 (5) Expansion of an ideal gas into vacuum through a pinhole is spontaneous process.

 All the above spontaneous processes becomes non-spontaneous when we reverse them by doing work.

 Spontaneous process and Enthalpy change : A spontaneous process is accompanied by decrease in internal energy or enthalpy, i.e., work can be obtained by the spontaneous process. It indicates that only exothermic reactions are spontaneous. But the melting of ice and evaporation of water are endothermic processes which also proceeds spontaneously. It means, there is some other factor in addition to enthalpy change \[(\Delta H)\] which explains the spontaneous nature of the system. This factor is entropy.