Question

5. Which of the following statements regarding spontaneous changes is false? A. Spontaneity is favored when heat is released. B. Spontaneity is favored when the dispersal of matter is increased. C. Spontaneous changes occur at a given state without any outside influence. D. Ice melting at 25°C is spontaneous primarily due to the increase in molecular disorder (dispersal of matter). E. All exothermic reactions are spontaneous.

Answer 1

Correct option: E

From the second law of thermodynamics,

AG = AH-TAS

Where, $\Delta G$ = change in Gibbs free energy, $\Delta H$ = change in enthalpy, $\Delta S$ = change in entropy of the reaction.

Now, $\Delta G$ is negative for a spontaneous process.

For exothermic reactions, $\Delta H$ is negative.

Now, if $\Delta S$ is also negative, then is positive.

-TAS

Given these conditions, if   
ΤΔS > ΔΗ
then, $\Delta G$ is positive.  

Hence, all exothermic reactions are not spontaneous.