Question

Suppose a scientist made a claim that all spontaneous reactions are exothermic. Whic of the following would provide the strongest challenge to their claim? Suppose a scientist made a claim that all spontaneous reactions are exothermic. Which of the following would provide the strongest challenge to their claim?
a. An exothermic reaction which is not spontaneous
b. An endothermic reaction that only proceeds when coupled to an exothermic reaction
c. An endothermic reaction that only proceeds when a catalytst is present
d. An endothermic reaction which is not spontaneous
e. All of the above

Answer 1

Answer: Option (c) is the correct answer.

Explanation:

It is given that the scientist is claiming that all the spontaneous reactions are exothermic in nature.

And, it is known that when a reaction is spontaneous in nature then $\Delta G$ is negative.

Now, the relation between Gibb's free energy, enthalpy and entropy is as follows.

               $\Delta G$ = $\Delta H - T \Delta S$

So, when a catalyst is present in a chemical reaction then we do not need to give large amount of heat from outside. And, because of this the enthalpy of reaction will not be highly positive.

Hence, the value of $\Delta G$ will result in a negative value which means the reaction is spontaneous.

Thus, we can conclude that an endothermic reaction that only proceeds when a catalytst is present, would provide the strongest challenge to their claim.