Final answer:
A given chemical reaction under standard conditions is characterized by a single standard free energy change. However, under non-standard conditions, the free energy change can vary due to multiple combinations of conditions. The equilibrium constant is fixed at a given temperature, unlike the reaction quotient, which can have infinite values before reaching equilibrium.
Step-by-step explanation:
It is true that for a given reaction carried out under standard conditions, there is only one value of standard free energy change (ΔG°). This is because standard conditions refer to a specific set of parameters: a pressure of 1 bar and a concentration of 1 M for solutions, typically at a temperature of 298.15 K, unless otherwise noted. In contrast, the free energy change for a reaction under non-standard conditions (ΔG) can have many values, reflecting the infinite combinations of pressures, concentrations, and temperatures that might apply.
The concept of equilibrium also illustrates this point. The equilibrium constant (K) for a reaction at a given temperature is fixed and is related to the standard free energy change. However, the reaction quotient (Q), which describes the ratio of product concentrations to reactant concentrations at any point in the reaction before it reaches equilibrium, can take on any number of values depending on the current state of the reaction mix. This is why there can be an infinite number of Q values but only one value for K at a particular temperature.