Activation energy depends on reaction pathway, altered only by catalysts

Steps:

• Activation energy (Ea) is the energy barrier for the reaction, determined by the pathway.
• Catalysts lower Ea by offering a lower-energy alternative route.
• Removing the catalyst reverts to the original, higher Ea pathway.
• Pressure and temperature changes affect collision frequency or energy distribution but not Ea.

Why B is correct:

• Catalysts reduce Ea per transition state theory; removal restores the uncatalyzed, higher Ea.

Why the others are wrong:

• A: Increases reactant concentrations, raising rate via collision theory but Ea unchanged.
• C: Alters nitrogen concentration, affecting equilibrium shift and rate but not Ea.
• D: Raises kinetic energy of molecules, increasing rate per Arrhenius equation (k = Ae^(-Ea/RT)) but Ea fixed.

Final answer: B