Gibbs Free Energy for non-standard conditions

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SUMMARY

The Gibbs Free Energy equation for non-standard conditions is expressed as ΔG=ΔG°+RTlnQ, where Q represents the reaction quotient. In this context, Q can be either Qp, based on the partial pressure of gases, or Qc, based on the concentration of solutes. Standard conditions vary for different states of matter: gases are at a fugacity of 1 bar, solutes at an activity of 1 mol/kg, and pure solids and solvents are considered at their standard states. Understanding these distinctions is crucial for accurate thermodynamic calculations in both chemistry and biological systems.

PREREQUISITES
  • Understanding of Gibbs Free Energy and its significance in thermodynamics
  • Familiarity with the concepts of reaction quotient (Q) and standard conditions
  • Knowledge of fugacity and its relation to partial pressure in gases
  • Basic principles of chemical equilibria and activities in solutions
NEXT STEPS
  • Study the differences between Qp and Qc in thermodynamic calculations
  • Research the implications of standard conditions in biological systems
  • Explore the concept of fugacity and its applications in gas-phase reactions
  • Learn about the role of activities in solution chemistry and their impact on Gibbs Free Energy
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Chemists, biochemists, and students studying thermodynamics who seek to understand the implications of non-standard conditions on Gibbs Free Energy calculations.

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ΔG=ΔG°+RTlnQ are for reactions that are not under standard conditions. What does it mean under non-standard conditions for the ΔG?

And what is the Q in this case? Is it Qp where it is based on the partial pressure of the gas or Qc which is based on the concentration?

Thanks
 
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Standard conditions are a convention and differ for solids liquids and gasses, as well as for solutes and solvents. Also, in biological systems other standard conditions are chosen than in chemistry.
A gas is under standard conditions when its fugacity (which is equal to its partial pressure in a good approximation for not too high pressures) is 1 bar. For a solution, standard condition of the solute is an activity of 1 mol/kg. For the solvent, the standard state is the pure solvent. For a solid, the pure solid.
 

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