Question

What are some common mistakes students make with non-spontaneous processes?

Answer 1

‘A chemical reaction in which the standard change in free energy is positive and energy is absorbed is known as an endergonic reaction (also known as a nonspontaneous reaction or an unfavourable reaction). The entire quantity of energy is a loss (it takes more energy to initiate the reaction than it gives back), thus the total energy is negative. Endergonic reactions can also be pushed by connecting them through a common intermediate to a highly exergonic reaction. The New Yorker's Saul Steinberg depicts a nonspontaneous process here.

Complete answer:
The first error is to believe that these changes are impossible.
The second error is to believe that any process that is slowed is non-spontaneous.
The third mistake is to believe that endothermic reactions are forced.
A non-spontaneous or endoergonic process is one that cannot proceed without the assistance of an external source.
However, with external intervention (first error), it is feasible (energy inputs, or coupling with other processes). Water decomposition, for example, is a non-spontaneous process. It can't happen unless there's an external source of energy (very high temperature or electrical forces, as in electrolysis)
We can wait for a long period if we take hydrogen and oxygen and combine them in a closed vessel, but no water forms. The reaction should be spontaneous, in contrast to the non-spontaneous reaction in the preceding case, yet it fails to begin. We shouldn't jump to the conclusion that this reaction is non-spontaneous (second error), because the next case is quite similar. We should expect a piece of paper to react spontaneously with oxygen, but this does not occur. Why don't you try it? Is this a non-spontaneous process? Not at all.
These reactions are just too slow to be observable at ambient temperature, but when ignited with a little spark or flame, they begin going rapidly, providing enough thermal energy to be self-sustaining and even going along spontaneously.
Not all endothermic reactions are non-spontaneous (third mistake). They can also happen in a closed system with no external input. You may put a fizzing powder in water and see how the water temperature drops, since the process is spontaneous, and everything happens on its own, even if the reacting combination is sealed in a container.

Note:
When reactions result in a drop in enthalpy and a rise in entropy, they are considered beneficial. The reaction happens spontaneously when both of these criteria are satisfied. A spontaneous reaction is one in which the creation of products is favoured under the conditions of the reaction. Because it is exothermic, a roaring campfire is an example of a spontaneous reaction (there is a decrease in the energy of the system as energy is released to the surroundings as heat). Combustion processes are spontaneous because of the combination of energy loss and entropy rise.