Final answer:
A process will be spontaneous when ΔG, the Gibbs free energy change, is negative. This indicates that the reaction can proceed without external energy input, with a negative ΔG suggesting a favorable process under standard conditions or at any temperature if ΔH is negative and ΔS is positive.
Step-by-step explanation:
A process will be spontaneous when ΔG is negative. The spontaneity of a reaction is based on the sign of the Gibbs free energy change (ΔG). According to the Gibbs free energy equation, processes with a ΔG less than 0 are spontaneous. This means they can occur without needing to be driven by an external force. Conversely, if ΔG is greater than 0, the process is not spontaneous and would need external energy to occur. However, it would occur spontaneously in the reverse direction.
The standard cell potential (E) and the equilibrium constant (K) are also indicators of spontaneity. If ΔG is <0, E is greater than 0 and K is greater than 1, indicating the direction of the reaction is spontaneous in the forward direction. We can also look at the enthalpy change (ΔH) and entropy change (ΔS). If ΔH is negative and ΔS is positive, this will result in a negative ΔG, leading to a spontaneous process at all temperatures due to both driving forces favoring product formation. Understanding these relationships helps in predicting the direction and spontaneity of chemical reactions.