Relation between gibbs free energy and equilibrium constant

In summary, the conversation discusses the derivation of the Nernst equation and its application in solving thermodynamic problems. The equation ΔG = ΔG° + RT ln(Q) is used to derive the Nernst equation, and the gas constant (R), Avogadro's number, and Boltzmann's constant are all involved in calculating ΔG for solutions. The conversation also mentions a discussion on the equivalence of ΔG for two different equations, and provides an example using the reaction N2 + 3H2 --> 2NH3 to show their agreement.
  • #1
HARI A
4
0
I am familiar with the equation ΔG=ΔG°+RT ln(Q).But I can't derive it.We have to use the equation to derive nernst equation. So please help.
 
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  • #2
I don't remember the derivation of the above equation off the top of my head, but I'm sure you can google it or look in any intro to the Thermodynamics or Physical Chemistry text.

As far as deriving the Nernst equation from what you have:

ΔG = -nFE and ΔG° = -nFE°

plug those two into ΔG = ΔG° + RTlnQ and do some simple algebraic rearranging.

This may not be useful to you if you are in an advanced class which requires derivations of the equations that I have taken for granted. In other words this is a pseudo-derivation applicable to a freshman level Gen. Chem. course.
 
  • #3
In this reference , post #2 PhaseShifter states: q = Keq
Can someone show how this is ?
https://www.physicsforums.com/showthread.php?t=332342
Also how does R the gas constant , Avogadro's number x Boltzamann's constant,
apply to ΔG for solutions ?
 
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  • #4
morrobay said:
In this reference , post #2 PhaseShifter states: q = Keq
Can someone show how this is ?

Do you know what Q is? (To be honest using q is IMHO confusing).
 
  • #5
Borek said:
Do you know what Q is? (To be honest using q is IMHO confusing).

Thanks, was looking at q as in heat. There is not a question on the equivalence of ΔG for
ΔG = -RTlnKeq and ΔG = ΔH - TΔS as Ill show for anyone who wants to see it
N2 + 3H2 --> 2NH3
Keq = (NH3)2/(N2)(H2)3 = 6.73 * 105 , lnK=13.4 , RT= 2.473 kJ/m So ΔG = -RTlnK = -33kJ/m
In agreement with ΔG = ΔH - TΔS
ΔH = -92kJ/m, T = 298K , ΔS = -198J/m
-33kJ/m = -92kJ/m + 59kJ/m
 
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1. What is the relationship between Gibbs free energy and equilibrium constant?

The relationship between Gibbs free energy and equilibrium constant is described by the following equation: ΔG = -RTlnK, where ΔG is the change in Gibbs free energy, R is the gas constant, T is the temperature in Kelvin, and K is the equilibrium constant. This equation shows that the equilibrium constant is directly proportional to the Gibbs free energy change.

2. How does Gibbs free energy affect the direction of a chemical reaction?

Gibbs free energy determines the spontaneity of a chemical reaction. A negative ΔG indicates that the reaction is spontaneous and will proceed in the forward direction. Conversely, a positive ΔG indicates that the reaction is non-spontaneous and will proceed in the reverse direction. When ΔG is equal to zero, the reaction is at equilibrium.

3. Can Gibbs free energy be used to predict the feasibility of a reaction?

Yes, Gibbs free energy can be used to predict the feasibility of a reaction. A negative ΔG indicates that the reaction is thermodynamically favorable and will occur spontaneously. A positive ΔG indicates that the reaction is thermodynamically unfavorable and will not occur spontaneously. However, the kinetics of a reaction must also be considered in determining its feasibility.

4. How is the equilibrium constant affected by changes in temperature?

The equilibrium constant is affected by changes in temperature according to the equation lnK2/K1 = -ΔH/R(1/T2 - 1/T1), where K1 and K2 are the equilibrium constants at temperatures T1 and T2 respectively, ΔH is the enthalpy change, and R is the gas constant. This equation shows that the equilibrium constant is inversely proportional to temperature, meaning that an increase in temperature will lead to a decrease in the equilibrium constant.

5. Can the equilibrium constant be used to calculate the Gibbs free energy change of a reaction?

Yes, the equilibrium constant can be used to calculate the Gibbs free energy change of a reaction using the equation ΔG = -RTlnK. This equation allows us to determine the Gibbs free energy change at any temperature, as long as the equilibrium constant is known. However, it should be noted that the calculated ΔG will only be valid at the temperature for which the equilibrium constant was determined.

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