Activation Energy in Catalytic Decomposition

Steps:

• Examine the energy diagram for the catalyzed decomposition of NH3, showing stepwise energy changes.
• Identify the reactants' energy level as the starting point.
• Locate the highest energy point (transition state) in the first reaction step after the catalyst lowers the barrier.
• Measure the energy difference from reactants to this first transition state; this is the activation energy for the first step.

Why D is correct:

• D labels the vertical distance from reactant energy to the first transition state peak, matching the definition of activation energy as the minimum energy required to initiate the reaction (Arrhenius equation: rate constant depends on e^(-Ea/RT)).

Why the others are wrong:

• A represents overall reaction energy change, not the first step's barrier.
• B indicates the second step's activation energy, beyond the first step.
• C shows the catalyzed overall activation energy, not specific to the first step.

Final answer: D