Under standard state conditions, what is the value of the reaction quotient Q in the Nernst equation?

• A. 0
• B. e
• C. 1
• D. Infinity

Answer: (C)

Q is the reaction quotient, defined as the activities of products divided by the activities of reactants, each raised to their stoichiometric powers. Under standard state conditions, every species has its standard activity set to 1 (1 for solutes at 1 M, 1 atm for gases, 1 for pure solids/liquids). With all activities equal to 1, the quotient becomes 1. This is also why the Nernst equation reduces to E = E° under standard conditions, since ln Q = ln 1 = 0. Values like 0 or infinity would require zero or infinite activities, which aren’t part of the standard-state definition, and a value of e would correspond to ln Q = 1, which isn’t the case here.