Question

A spontaneous process may be defined as:
(A) A process which is exothermic and evolves a lot of heat
(B) A process which is slow and reversible
(C) A process which takes place only in presence of a catalyst
(D) A process that occurs without any input from the surroundings

Answer 1

In thermodynamics the value of $\Delta G$ is negative in the case of spontaneous processes. That means that the energy is released in the reaction. Non-spontaneous reactions require some input from outside in order to make a reaction occur.

Complete step by step solution:
Let’s know something about spontaneous processes.
- A spontaneous process is a process which occurs without any input from outside.
- In this process, the system releases the energy and becomes more stable thermodynamically. Here, the release of the free energy corresponds to a negative in the free energy of the system.
- Thus, we can say that the spontaneous processes need not to be driven by outside sources.
- In thermodynamics, we can say that if $\Delta G$ value is negative, then the process will occur without any input from surrounding and thus it is a spontaneous process. If the $\Delta G$ value is positive, then the process is called a non-spontaneous process. So, we need to give some energy from outside to make those reactions occur.
- For most of the cases, it is said that the entropy of the system increases during the spontaneous reaction.
-Thus, we can say that spontaneous process is a process that occurs without any input from the surroundings.

Therefore, the correct answer of this question is (D).

Note: The process in which diamond is converted to graphite is a spontaneous process at normal room temperature and pressure. Now, despite it being a spontaneous process, the reaction does not occur. This happens because the energy required to break the carbon-carbon bonds is larger than the release in free energy.