Question

which is true about reaction rates?
○ high reaction rates occur only in spontaneous reactions.
○ low reaction rates occur only in nonspontaneous reactions.
○ reaction rates are not dependent on high or low activation energies.
○ reaction rates are not related to spontaneity.

Explanation:

• Spontaneity (whether a reaction is spontaneous or non - spontaneous) is about the thermodynamic favorability of a reaction (related to Gibbs free energy change, $\Delta G$). Reaction rate is about how fast a reaction occurs (related to activation energy, collision frequency, etc.). A spontaneous reaction can have a slow rate (e.g., rusting of iron is spontaneous but slow), and a non - spontaneous reaction can have a fast rate if sufficient energy is provided.
• The first option is wrong because a spontaneous reaction can have a low rate (e.g., diamond turning to graphite is spontaneous but very slow).
• The second option is wrong because a non - spontaneous reaction's rate isn't determined solely by its non - spontaneity; with enough energy input, it can have a high rate.
• The third option is wrong because activation energy is a key factor in reaction rate (the Arrhenius equation shows the relationship between rate constant and activation energy: $k = A e^{-\frac{E_a}{RT}}$).
• The fourth option is correct because reaction rate (kinetics) and spontaneity (thermodynamics) are independent concepts.

Answer:

D. Reaction rates are not related to spontaneity.