How Does Temperature Affect Equilibrium Constants for Conformers?

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SUMMARY

The discussion focuses on calculating the equilibrium constants (Keq) for two conformers with a 1 Kcal/mol energy difference at room temperature (293.15 K) and at -78°C (195.15 K). The correct formula used is Keq = e^(ΔG/(-R*T)), where R is the gas constant (8.313 J/(mol*K)). The user initially calculated Keq values of 0.18 at room temperature and 0.08 at -78°C but was informed that they mistakenly used the wrong ΔG value. The correct approach requires using the standard ΔG for the reaction rather than the change in ΔG.

PREREQUISITES
  • Understanding of thermodynamics and Gibbs free energy.
  • Familiarity with the concept of equilibrium constants (Keq).
  • Knowledge of the gas constant (R) and its units.
  • Basic proficiency in logarithmic functions and exponential equations.
NEXT STEPS
  • Review the derivation of the Gibbs free energy equation in thermodynamics.
  • Learn about the relationship between temperature and equilibrium constants.
  • Explore the implications of conformational energy differences on reaction equilibria.
  • Study the effects of temperature on reaction kinetics and thermodynamic properties.
USEFUL FOR

Chemistry students, researchers in thermodynamics, and anyone studying the effects of temperature on chemical equilibria will benefit from this discussion.

krootox217
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Homework Statement


Hi, I have the following task:

We have two conformers and the difference in energy between them is aprox. 1 Kcal/mol. What is the Keq at room temperature vs. at -78°C?

Homework Equations



Keq=e^(deltaG/(-R*T))

The Attempt at a Solution



I tried to solve the problem the following way:

deltaG = R*T*ln(Keq) --> Keq=e^(deltaG/(-R*T))

T(room)=293.15K, T(-78°C)=195.15K
R=8.313 J/(mol*K), DeltaG= 1 Kcal/mol= 4184 J/mol

then I inserted the values and got Keq(room) = 0.18 and Keq(-78°C) = 0.08 which is apparently wrong. They told me that I used deltadeltaG instead of deltaG in the equation. Can somebody help me?
 
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In the equation you quote, how is ΔG defined?
 

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