Enzymes lower activation energy without altering reaction enthalpy

Steps:

• Enzymes act as catalysts, reducing the activation energy (Ea) required for reactions.
• Activation energy appears as the energy barrier peak in reaction coordinate diagrams.
• Adding an enzyme lowers this peak while keeping overall energy change (ΔG) unchanged.
• Identify the graph showing decreased Ea peak with unchanged reactant/product levels.

Why D is correct:

• D depicts a lowered activation energy barrier, aligning with the catalytic definition that enzymes provide an alternative pathway with lower Ea.

Why the others are wrong:

• A shows unchanged Ea, ignoring enzyme catalysis.
• B incorrectly lowers product energy, altering ΔG.
• C raises Ea, opposite to enzyme effect.

Final answer: D