I recently took a Gen. Chem. 2 exam that contained this question. I answered false, as I knew that thermodynamics and kinetics are separate matters. My professor said the answer is true. I pressed him on it, citing a specific portion of our textbook that stated that the spontaneity of a reaction must not be conflated with the reaction rate. He admitted that it's true that a highly negative ∆G value does not necessarily imply that a reaction will be fast, but he said that that's usually the case, so I should have answered "true". This strikes me as absurd, not only because it's not a reasonable interpretation of a true/false question (they're supposed to be interpreted strictly, and if there's no qualifier like "generally" or "typically", then an if/then proposition should be treated as a "necessarily true" claim), but also because most students probably answered "true" because they did conflate spontaneity with reaction rate, which is something the textbook specifically warned against.
My professor also sent me the following via email:
"Please note that delta G combines all the properties of thermodynamics, which includes kinetics. Delta G has two components. Delta H (enthalpy) and Delta S (entropy). A large negative delta H means the reaction is highly exothermic. A large positive delta S means the product "randomness" is highly favorable, the system wants to happen even if enthalpy isn't high. I know of no system with these two feature that isn't fast. Note: rust (iron + oxygen going to rust) is highly exothermic, but the delta S is negative (solid and gas going to a solid), and that's why the reaction is favorable but slow."
I was surprised by this, as it directly contradicts what our textbook says on the matter. My understanding is that the ∆G equation contains only thermodynamic state variables and simply expresses the magnitude of thermodynamic potential. I see nothing in the equation that could convey information about the rate at which a process happens.
I would greatly appreciate not only theoretical comments on this, but also some specific examples of reactions with "large negative ∆G values" that are not "fast". (The inherent ambiguity of the terms "large" and "fast" here also seems to be a problem.)