26: Chemical Equilibrium
- Page ID
- 11822
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- 26.1: Equilibrium Results when Gibbs Energy is Minimized
- For a chemical reaction, the system will reach equilibrium when the Gibbs energy is minimized as a function of the extent of reaction.
- 26.2: An Equilibrium Constant is a Function of Temperature Only
- The equilibrium constant, \(K\), is a function of temperature, \(T\), and not pressure, \(P\), or composition.
- 26.3: Standard Gibbs Energies of Formation Can Be Used to Calculate Equilibrium Constants
- The standard Gibbs energy of formations can be used to calculate the standard Gibbs energy of any reaction. The standard Gibbs energy of reaction can then be used to calculate the equilibrium constant through the expression \(K=e^{-\frac{\Delta_rG^\circ}{RT}}\).
- 26.4: Gibbs Energy of a Reaction vs. Extent of Reaction is a Minimum at Equilibrium
- We can relate thermodynamic quantities to concentrations of molecules and we can see that there will be a characteristic ratio of concentration of reactants and products that will exist for any reaction called the equilibrium constant.
- 26.5: Reaction Quotient and Equilibrium Constant Ratio Determines Reaction Direction
- The reaction quotient (\(Q\)) measures the relative amounts of products and reactants present during a reaction at a particular point in time. The reaction quotient aids in figuring out which direction a reaction is likely to proceed, given either the pressures or the concentrations of the reactants and the products. The \(Q\) value can be compared to the Equilibrium Constant, \(K\), to determine the direction of the reaction that is taking place.
- 26.6: The Sign of ΔG and not ΔG° Determines the Direction of Reaction Spontaneity
- \(\Delta G^\circ\) represents conditions only at standard state conditions, while \(\Delta G\) represents the Gibbs energy at any conditions. Therefore, it is \(\Delta G\), and not \(\Delta G^\circ\), that determines the direction of spontaneity.
- 26.7: The van 't Hoff Equation
- The expression for equilibrium constant is a rather sensitive function of temperature given its exponential dependence on the difference of stoichiometric coefficients. A linear relation between ln K and the standard enthalpies and entropies can be constructed and is known as the van’t Hoff equation.
- 26.8: Equilibrium Constants in Terms of Partition Functions
- We can use statistical mechanics to calculate equilibrium constants in terms of molecular parameters.
- 26.9: Molecular Partition Functions and Related Thermodynamic Data Are Extensively Tabulated
- Calculating highly accurate equilibrium constants can often involve laborious calculations. To decrease the need to perform such calculations, partition functions and related thermodynamic data from experiments are extensively tabulated in JANAF tables.
- 26.10: Real Gases Are Expressed in Terms of Partial Fugacities
- The relationship for chemical potential was derived assuming ideal gas behavior. But for real gases that deviate widely from ideal behavior, the expression has only limited applicability. In order to use the simple expression on real gases, a “fudge” factor is introduced called fugacity. Fugacity is used instead of pressure.