G naught doesnt tell you whether the reaction is spontaneous or not
Yes, it will if the reaction is carried out under "standard conditions" and the temperature is 298.15 K.
To determine whether a reaction is spontaneous or not, you should consider the sign of the change in Gibbs free energy (ΔG). ΔG is related to the equilibrium constant (K) for the reaction via the equation ΔG° = -RT ln(K), where R is the gas constant and T is the temperature.
The standard Gibbs free energy change, ΔG°, is the change in Gibbs free energy under standard conditions, which are defined to be 298 K and 1 bar pressure. So, ΔG° is calculated using the standard free energy of formation of the reactants and products.
If ΔG° is negative, it means that the reaction is spontaneous in the forward direction under standard conditions. This suggests that the reaction will proceed without the need for external input of energy. On the other hand, if ΔG° is positive, it means that the reaction is non-spontaneous under standard conditions and will require an input of energy for it to occur.
However, it is important to note that the sign of ΔG° alone does not give information about the spontaneity of a reaction under non-standard conditions. To fully determine the spontaneity of a reaction under different conditions, you would need to calculate the actual value of ΔG (not just ΔG°) using the equation ΔG = ΔG° + RT ln(Q), where Q is the reaction quotient.
By comparing ΔG with zero, you can determine if the reaction is spontaneous in a particular direction (ΔG < 0), at equilibrium (ΔG = 0), or non-spontaneous (ΔG > 0). Hence, while G° (G naught) provides standard information about the spontaneity of a reaction, the actual value of ΔG under specific conditions determines whether a reaction is spontaneous or not.