Question

Identify the correct statement regarding a spontaneous process

1. For a spontaneous process in an isolated system, the change in entropy is positive
2. Endothermic process is never spontaneous
3. Exothermic processes are always spontaneous
4. Lowering of energy in the reaction process is the only criterion for spontaneity

Answer 1

To understand the question, students should be familiar with the thermodynamics nature of reactions and its different properties. Thermodynamics deals with the relationships between heat and other forms of energy. In particular, it describes how thermal energy is converted to and from other forms of energy and how it affects matter.

Complete answer:
Option (1)
The second principle of thermodynamics says that in an isolated system, the change in entropy can only be positive or equal to zero. Hence for a spontaneous process in an isolated system, the change in entropy is positive.
Therefore, option (1) is correct.
Option (2)
Endothermic reactions with negative $\Delta S$ are never spontaneous. Endothermic reactions with positive $\Delta S$ are non-spontaneous at low temperatures but become spontaneous at high temperatures.
Therefore, option (2) is incorrect.
Option (3)
The same reason applies for exothermic reactions. Spontaneity can only be achieved under the right temperature.
Therefore, option (3) is incorrect.
Option (4)
Lowering of energy in the reaction process is not the only criterion for spontaneity. It can also be achieved through the right temperature.
Therefore, option (4) is incorrect.
Therefore, option (1) is correct.

Note:
The second law of thermodynamics is understood by the equation of Gibbs free energy which is $\Delta G = \Delta H - T\Delta S$ . Here, $\Delta S$ is the change in entropy and $T$ is the absolute temperature in $K$ . This expression may be positive even with a negative enthalpy change (exothermic process) if the entropy change is negative and the temperature is high enough.