Question

Which of the following processes is nonspontaneous?
A. Heat flow from hot end to cool end
B. Water flow from higher level to lower level
C. Gas flow lower pressure region to higher pressure region
D. Gas flow higher pressure region to lower pressure region

Answer 1

A process which occurs in a given direction without the help of any outside source of energy is called a spontaneous process or a natural process. A process which does not occur naturally but with the help of an external force is called a non-spontaneous process.

Complete step by step answer:
Gas flow lower pressure region to higher pressure region – Gases do not flow from a lower pressure region to a higher pressure region naturally. For gases to flow in this manner, an external force is required. Hence, this process is nonspontaneous.
So, the correct answer is “Option C”.

Additional information:
Heat flows from hot end to cool end – Heat always flows from the hot end to the cool end until a state of equilibrium is reached, that is, the temperature of both ends become equal and therefore, no more heat is transferred. This process occurs without the help of any external force. This is a natural phenomenon and hence, spontaneous.
Water flows from higher level to lower level – Water always flows from a higher level to a lower level due to the force of gravity. Since, the force of gravity is a natural force and is applied to all objects on Earth, this phenomenon is also natural and hence, spontaneous.
Gas flows from higher pressure regions to lower pressure regions – Gases always flow from a higher pressure region to a lower pressure region due to the random movement of particles. This process does not require any external force and occurs naturally. Hence, this is a spontaneous process.

Note: The reverse of a spontaneous process is always nonspontaneous. For example, melting of ice is spontaneous but freezing of ice is not.