Catalysts lower activation energy in reactions

Steps:

• Activation energy (Ea) is the energy barrier reactants must overcome to form products.
• Catalysts speed up reactions by offering an alternative pathway with reduced Ea.
• Temperature, concentration, and pressure influence reaction rate via collision theory but do not alter Ea.
• For the ammonia synthesis, only a catalyst directly lowers Ea.

Why A is correct:

• A catalyst decreases activation energy by providing a lower-energy reaction pathway, as defined in chemical kinetics (Arrhenius equation: rate constant k = A e^(-Ea/RT)).

Why the others are wrong:

• B: Decreasing temperature reduces molecular kinetic energy, slowing the rate but leaving Ea unchanged.
• C: Increasing concentration raises collision frequency, boosting rate without affecting Ea.
• D: Increasing pressure compresses gases, effectively raising concentration and rate, but Ea remains the same.

Final answer: A