Question

A chemical reaction is spontaneous at 298 K but non-spontaneous at 350 K. Which one of the following is true for the reaction?
A. $\Delta G(-)$, $\Delta H(-)$,$\Delta S(+)$
B. $\Delta G(+)$,$\Delta H(+)$,$\Delta S(+)$
C. $\Delta G(-)$ ,$\Delta H(+)$,$\Delta S(-)$
D. $\Delta G(+)$,$\Delta H(-)$,$\Delta S(+)$
E. $\Delta G(-)$,$\Delta H(-)$,$\Delta S(-)$

Answer 1

Spontaneous processes are generally studied by the branch called thermodynamics which is related to heat, work, temperature and energy changes during the processing of reactions. Spontaneous process is defined as the time evolution of a system in which a large amount of energy is released and it moves itself to a stable energy state.

Complete step-by-step answer:
A reaction which occurs at constant temperature and pressure then spontaneity can be described in the terms of change in Gibbs free energy which can be explained as a thermodynamic potential which is used to calculate the maximum reversible work that may be performed by a thermodynamic system at a constant temperature and pressure.
The equation is for change in Gibbs free energy is given by: $\Delta H>0$ $\Delta G=\Delta H-T\Delta S$
Where $\Delta G$= Change in Gibbs free energy, $\Delta H$= change in enthalpy and $\Delta S$= change in entropy. Spontaneity of the system depends on these terms if $\Delta G$ is negative then the process is spontaneous in nature if positive then non-spontaneous. When $\Delta S>0$ and $\Delta H<0$ then the process is always spontaneous but if the reverse happens i.e. $\Delta S<0$ and $\Delta H>0$ then the process is never spontaneous. Now if we say that $\Delta H$ and $\Delta S$ both are greater than zero then the process will be spontaneous at high temperatures and non-spontaneous at low temperatures and if both are less than zero then the process will be spontaneous at low temperatures and non-spontaneous at high temperatures.
Hence from the above discussion we conclude that all the terms should be less than zero for being non-spontaneous in nature i.e. have to be negative.

Thus, option E is the correct answer.

Note: In general the spontaneity of a process is only used to determine whether a process can occur or not. In simple manner we can also say that spontaneity is necessary but not sufficient condition for a process to actually occur.