Chemical kinetics fundamentals: The extra energy that reactant molecules must acquire to transform into products is termed what kind of energy?

Introduction / Context:
Reaction rates depend on the fraction of molecules energetic enough to pass over the energy barrier separating reactants from products. This barrier height is a key kinetic parameter widely used in Arrhenius-type rate expressions.

Given Data / Assumptions:

• Molecular collisions are required for reaction.
• Only collisions with sufficient energy and proper orientation are effective.
• We are identifying the common kinetic term for this energy requirement.

Concept / Approach:
The Arrhenius equation, k = A * exp(-Ea / (R*T)), contains Ea, called the activation energy. It represents the minimum additional energy that reactants must gain to reach the transition state, after which transformation to products is much more probable.

Step-by-Step Solution:
Recognize that not all collisions are reactive.Define the energetic hurdle as activation energy, Ea.Relate to temperature sensitivity: higher T increases the fraction of molecules with energy ≥ Ea, thus increasing k.

Verification / Alternative check:
Straight-line plots of ln k versus 1/T have slope −Ea/R, empirically confirming the activation energy concept for many reactions.

Why Other Options Are Wrong:

• Potential or binding energy: general terms not specific to the kinetic barrier.
• Threshold energy (as used generically) is not the standard kinetic parameter; the accepted term is activation energy.

Common Pitfalls:
Confusing thermodynamic favorability (ΔG) with kinetic accessibility (Ea). A reaction can be exergonic yet slow if Ea is large.

Final Answer:
Activation energy