Question

Reaction A HAD an activation energy of 50 kJ/mol, and reaction B has an activation energy of 120 kJ/mol
which reaction is more likely to occur at room temperature, and why

Answer 1

Reaction A. A lower activation energy means a much larger fraction of molecules have enough energy to react at a given temperature.

Using the Arrhenius form k = A exp(−Ea/RT) (T ≈ 298 K), and assuming similar pre-exponential factors A, the relative rate is roughly

kA/kB ≈ exp[(Ea,B − Ea,A)/(RT)] = exp[(120 − 50) kJ·mol−1/(8.314×10−3 kJ·mol−1·K−1 × 298 K)]
≈ exp(70 000/(8.314×298)) ≈ exp(≈28) ≈ 10^12.

So reaction A would be on the order of a trillion times faster at room temperature (assuming similar frequency factors). Practical caveats: the actual rate also depends on the pre‑exponential factor, mechanism, concentrations, and any catalyst, but lower Ea strongly favors reaction A at room temperature.