Final answer:
The spontaneity of a reaction at 298 K is determined by the Gibbs free energy change (ΔG), calculated by the formula ΔG = ΔH - TΔS. The reaction is spontaneous if ΔG is negative. Activation energy does not determine spontaneity; it is the combined effect of enthalpy and entropy changes that matters.
Step-by-step explanation:
The question of what determines whether a reaction is spontaneous at 298 K revolves around the concept of Gibbs free energy change (ΔG).
To determine spontaneity, one calculates ΔG using the formula ΔG = ΔH - TΔS, where ΔH is the enthalpy change and ΔS is the entropy change of the reaction, and T is the temperature in Kelvin. A reaction is considered spontaneous if ΔG is negative, non-spontaneous if it is positive, and in equilibrium if it is zero.
It is important to note that while the activation energy is crucial for a reaction to start, it does not determine spontaneity. Similarly, enthalpy (ΔH) and entropy (ΔS) alone do not exclusively determine spontaneity; it is their combined effect on Gibbs free energy that is decisive. At 298 K, a spontaneous reaction will have a ΔG value less than zero.
Considering the temperature dependence of spontaneity, the relationship between ΔG, ΔH, and ΔS can shift with temperature changes. For instance, a reaction may become spontaneous at a certain temperature if the TΔS term becomes large enough to override a positive ΔH, resulting in a negative ΔG.