what is the difference between these two equation:
delta G= delta H-T(delta S)
and deltaG(knot)=delta H(knot)-T(delta S knot)
Which G do i use to tell whether the reaction is spontaneous
To understand the difference between these two equations and determine which one to use to determine if a reaction is spontaneous, it is important to understand the variables and their meanings.
1. ΔG = ΔH - TΔS:
- ΔG represents the change in Gibbs free energy of the system.
- ΔH is the change in enthalpy (heat) of the system.
- T is the temperature in Kelvin.
- ΔS is the change in entropy of the system.
2. ΔG° = ΔH° - TΔS°:
- ΔG° represents the change in Gibbs free energy at standard conditions (1 atm pressure and 298 K temperature).
- ΔH° is the standard enthalpy change.
- T is the temperature in Kelvin.
- ΔS° is the standard entropy change.
The key difference between the two equations lies in the use of the symbol "°" (degree), which denotes standard conditions.
Now, to determine whether a reaction is spontaneous, you need to consider the sign of ΔG. If ΔG is negative (ΔG < 0), the reaction is spontaneous and can occur without the need for external energy. If ΔG is positive (ΔG > 0), the reaction is non-spontaneous under the given conditions and requires external energy to proceed. If ΔG is zero (ΔG = 0), the reaction is at equilibrium.
To evaluate the spontaneity of a reaction, you can use either equation. However, if you know the standard values of enthalpy (ΔH°) and entropy (ΔS°), and the reaction is taking place at standard conditions, you can use the equation ΔG° = ΔH° - TΔS°. This equation specifically applies to standard conditions.
On the other hand, if you know the actual values of ΔH and ΔS at non-standard conditions, you should use the equation ΔG = ΔH - TΔS to calculate ΔG.
In summary, to determine whether a reaction is spontaneous, you need to calculate ΔG using either equation depending on the available information regarding standard or non-standard conditions. A negative ΔG indicates a spontaneous reaction.