Relationship between free energy and the equilibrium constant

Click For Summary
SUMMARY

The relationship between free energy and the equilibrium constant is defined by the equation ΔG° = -RT ln K. In the discussion, the temperature-dependent Kb values for NH3(aq) were provided, showing variations at 283 K, 293 K, and 303 K. The discussion emphasized that ΔS° and ΔH° can be considered approximately temperature independent over moderate temperature ranges. Additionally, the correct formulation for plotting ln Kb against temperature involves using the equation ln Kb = ΔH/R - ΔS/R, where ΔH and ΔS are the reaction's enthalpy and entropy changes, respectively.

PREREQUISITES
  • Understanding of thermodynamics concepts, specifically free energy and equilibrium constants.
  • Familiarity with the Van 't Hoff equation and its application in chemical reactions.
  • Knowledge of how to measure and interpret pH and Kb values in aqueous solutions.
  • Basic graphing skills to plot ln Kb against temperature for analysis.
NEXT STEPS
  • Study the Van 't Hoff equation in detail to understand its implications on temperature and equilibrium constants.
  • Learn how to calculate ΔH° and ΔS° from experimental data using graphical methods.
  • Explore the effects of temperature on the solubility and dissociation constants of weak bases like NH3.
  • Investigate the relationship between pH, Kb, and free energy in various chemical systems.
USEFUL FOR

Chemistry students, researchers in thermodynamics, and professionals involved in chemical equilibrium studies will benefit from this discussion.

chazgurl4life
Messages
52
Reaction score
0
The relationship between free energy and the equilibrium constant is

Go = -RT ln K

By measuring the pH at various temperatures, the Kb for NH3(aq) was found to be temperature dependent, yielding the following values:

temperature (K) Kb
283 1.34 X 10-5
293 1.42 X 10-5
303 1.50 X 10-5

Over moderate temperature ranges (ranges less than 100 K degrees) both deltaSo and deltaHo can be considered approximately temperature independent. By plotting the available information appropriately, obtain estimates for deltaSo and delayHo for the reaction:


ok so i figured out that my y=mx+b equation should loook lik:

lnKb=delta H/R(gas constnt) - delta S/r

bbut what is my x-axis and y axis?
 
Physics news on Phys.org
1. This question belongs in the Coursework & Homework section of the forums. Henceforth, please post such questions there (and use a more descriptive title).

2.
ok so i figured out that my y=mx+b equation should loook lik:

lnKb=delta H/R(gas constnt) - delta S/r
That's not right. What is the relationship between \Delta G_0~,~~\Delta H_0 and \Delta S_0 ?
 
Last edited:

Similar threads

Chemistry Confusion in relation of Gibbs free energy and equilibrium constant
  • · Replies 4 ·
Replies
4
Views
3K
Chemistry A calculation of enthalpy, entropy, and Gibbs energy of vaporization
  • · Replies 1 ·
Replies
1
Views
2K
Esimating delta S and delta H from temp and Kb
  • · Replies 1 ·
Replies
1
Views
13K
Relationship between Free energy change and Equilibrium constant (K)
  • · Replies 3 ·
Replies
3
Views
3K
Chemistry How to reason about Gibbs energy change due to entropy not enthalpy?
  • · Replies 4 ·
Replies
4
Views
2K
Chemistry Create a Gibbs Free Energy challenge question
  • · Replies 1 ·
Replies
1
Views
3K
Physical Chemistry Homework: Equilibrium Constant and Gas Properties
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Identification of changes in internal energy with work (in Callen's Thermodynamics)
  • · Replies 5 ·
Replies
5
Views
1K
Equilibrium constant (K) Question problem
  • · Replies 1 ·
Replies
1
Views
3K
Calculating Entropy Change for N2O4 Equilibrium in Constant Pressure Vessel
  • · Replies 4 ·
Replies
4
Views
3K