Here are the essential concepts you must grasp in order to answer the question correctly.
Free Energy
Free energy, often represented as Gibbs free energy (G), is a thermodynamic potential that measures the maximum reversible work obtainable from a thermodynamic system at constant temperature and pressure. A decrease in free energy during a reaction indicates that the process can occur spontaneously, while an increase suggests nonspontaneity.
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Spontaneous Reactions
A spontaneous reaction is one that occurs without the need for external energy input. In an energy diagram, spontaneous reactions are typically represented by curves that show a decrease in free energy as the reaction progresses, indicating that the products are more stable than the reactants.
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Nonspontaneous Reactions
Nonspontaneous reactions require an input of energy to proceed, as they result in an increase in free energy. In energy diagrams, these reactions are depicted by curves that rise above the starting energy level, indicating that the products are less stable than the reactants and that energy must be supplied for the reaction to occur.
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