Explain why each of the following is incorrect:
(a) Entropy increases in all spontaneous reactions.
Wouldn't (a) be actually correct? Because when there's a spontaneous reaction, you have less stable molecules and more disorder. It will be lower in some reactions than in others, but doesn't it always increase when a reaction favors spontaneity?
So when there's a spontaneous reaction, deltaS is > 0 , I confused that with increase. I still don't see how it's incorrect
(b) deltaG < 0 , are product-favored and occur with rapid transformation of reactants to products.
HOw is this incorrect? deltaG < 0 is product-favored and is rxn forward.
Thank you
For dS, it depends upon what dS you are talking about. dS is positive(increases) for all spontaneous reactions IF you are talking about total dS; i.e.,
dSsurrounds + dSsystem = positive.
For dG, the first part is correct about < 0; the last part makes it incorrect. dG says nothing about how fast a reaction will occur.
Thanks Bob! As for deltaS, it just says Entropy increases in all spontaneous reactions, there's nothing more specified, so I assumed that it was deltaS and not deltaSuniverse
Regarding dS for the system, there are some reactions that occur spontaneously in which dS decreases. Since
dG = dH - TdS, the delta H part may override the TdS part just as in endothermic reactions the TdS part can overcome the dH part.
I get it now, thanks again Bob
Actually, the statement in (a) is incorrect. Entropy is a measure of the disorder or randomness in a system. While it is true that spontaneous reactions tend to increase entropy in the universe as a whole, this does not mean that entropy increases in all spontaneous reactions.
In thermodynamics, the change in entropy (∆S) of a system is determined by the difference between the entropy of the final state (Sf) and the entropy of the initial state (Si). The second law of thermodynamics states that the entropy of the universe tends to increase for spontaneous processes, but this does not necessarily mean that the entropy of the system always increases.
For example, in some spontaneous reactions, the entropy of the system may actually decrease, but there is a compensating increase in the entropy of the surroundings or the universe. This can occur when a reaction results in the formation of more organized or ordered products, such as the formation of crystals.
On the other hand, an increase in entropy in a spontaneous reaction is more common. This is because many spontaneous reactions involve the conversion of reactants into products that are more dispersed or have more degrees of freedom. For example, the dissolving of a solute in a solvent or the melting of a solid into a liquid generally results in an increase in entropy.
To determine whether entropy increases or decreases in a given spontaneous reaction, you would need to consider the overall change in entropy of both the system and the surroundings. This requires analyzing the physical and chemical properties of the reactants and products involved, as well as the conditions under which the reaction takes place.