Delta G Vs. Delta G Naught: Delta g is used to find Gibbs free energy in nonstandard conditions while Delta G naught is used to determine Gibbs free chemical reaction energy under normal conditions. The standard condition means the pressure 1 bar and Temp 298K, Delta G naught is the measure of Gibbs free energy. The energy associated with a chemical reaction that can be used to do work change at 1 bar and 298 K, Delta G naught is not necessarily a non-zero value. In other words, if product and reactant are equally favored at equilibrium, it’s because there is no difference. Delta G naught is always the same for a given reaction. But Delta G does depend on your conditions, but still relates to Delta H naught and Delta S naught. There are many differences between Delta G and Delta G naught, which are listed below:
So What is the Difference Between Delta G and Delta G Naught?
1. Delta G relate to these two quantities ΔH° and ΔS° while Delta G naught does not relate to the quantities:
Delta G definitely does relate to those two quantities. ΔH° and ΔS° represent the change in enthalpy and entropy between product and reactant but they do not mean a “100% complete reaction.” They determine the energetic difference (at a given temperature). This difference in energy determines the composition at equilibrium
2. Delta G is not a non-zero value while Delta G naught is a non-zero value
Delta G naught is a non-zero value and it can’t use ΔH° or ΔS° to find Delta G because either ΔH° or ΔS° represents 100% complete reaction.
3. At equilibrium Delta G is equal to zero while Delta G naught is negative:
If Delta G naught is negative at equilibrium, then we will have lots of products at equilibrium, which means that Q must be greater and also greater than 1 to approximate K. When Q gets bigger, it means more product is accumulated. The term ‘RT in Q’ gets increasingly positive, and eventually adding that term to a negative Delta G naught, will make Delta G = 0, equilibrium will be established and no further change occurs.
4. Equilibrium is established when Delta G is at zero while lots of reactant at equilibrium when Delta G naught is positive
If Delta G naught is positive at equilibrium, then we will have lots of reactants at equilibrium, meaning Q needs to be smaller (less than 1) to approach K. As Q gets smaller (i.e., as we get more reactants), the term ‘RT ln Q’ gets increasingly negative and eventually adding that term to a positive Delta G naught, will make Delta G = 0, equilibrium will be established and no further change occurs.
5. When Delta G is zero at equilibrium, it will define which way the reaction proceeds while Delta G naught does not
Note that it is Delta G and not Delta G naught that will be zero at equilibrium and the sign of it generated by the combination of Delta G naught and RT in Q, will define which way the reaction proceeds.