Catalysts Do Not Affect the Equilibrium Constant

Steps:

• Recall that the equilibrium constant K for N2 + 3H2 ⇌ 2NH3 depends only on temperature.
• A catalyst speeds up the forward and reverse rates equally, leaving the ratio of rate constants (K = k_forward / k_reverse) unchanged.
• Pressure and concentration changes shift the position of equilibrium per Le Chatelier's principle but do not alter K.
• Select the option that affects neither K nor the position: addition of a catalyst.

Why A is correct:

• Catalysts lower activation energies equally for forward and reverse reactions, preserving K as defined by the rate constant ratio.

Why the others are wrong:

• B: Specifies the iron catalyst used in the Haber process, but this is a distractor; the general principle applies to A.
• C: Increases pressure shifts equilibrium toward fewer gas moles (products), changing concentrations while K stays constant.
• D: Adds product (ammonia), shifting equilibrium left to restore K, thus changing concentrations.

Final answer: A