Identify the correct statement from the following in a chemical reaction

Options

A. The entropy always increases
B. The change in entropy along with suitable change in enthalpy decides the fate of a reaction
C. The enthalpy always decreases
D. Both the enthalpy and the entropy remain constant

Answer

B

Explanation

`Delta G= Delta H- T Delta S`
For first condition, reaction will be spontaneous at all temperatures. For second option as `Delta H` = +ve and `Delta S` is tue thus `Delta G = ubrace(Delta H)_(+ve) - ubrace(T Delta S)_((-ve))`
If temperature is high, `T Delta S` will have higher negative value and reaction will be spontaneous. Thus not true for given reaction. In case (c), `Delta G` = always positive
`rArr` non-spontaneous at all temperatures
In case (d), `Delta H = -ve, Delta S` = +ve
`rArr` spontaneous at all temperatures In case (e), `Delta G= ubrace(Delta H)_(-ve) - ubrace(T Delta S)_(+ve)`
At high temperature, second term will have high positive value and reaction will be non-spontaneous, thus case (e) is true for given example. `Delta G= Delta H- Delta S`
For a reaction to be spontaneous `Delta G` should be negative. Thus `Delta S and Delta H` decides the fate of a reaction.