gas-phase-chemical-equilibrium-summary

The answers to the ConcepTests are given below and will open in a separate window.

The equilibrium constant is dimensionless and is independent of pressure, but not of temperature.
The equilibrium composition is only independent of pressure if the number of gas-phase moles does not change in the reaction and the gases are ideal. If the number of gas-phase moles in the reaction increases, increasing the pressure at constant temperature decreases the equilibrium conversion. If the number of gas-phase moles in the reaction decreases, increasing the pressure at constant temperature increases the equilibrium conversion.
An inert gas can change the equilibrium conversion if the reaction involves a change in the number of gas-phase moles. If the number of gas-phase moles in the reaction increases, adding an inert gas at constant temperature and pressure increases equilibrium conversion (the same as decreasing the pressure). If the number of gas-phase moles in the reaction decreases, adding an inert at constant temperature and pressure decreases equilibrium conversion (the same as increasing the pressure).
For an exothermic reaction (ΔH < 0), as temperature increases, K decreases.
For an endothermic reaction (ΔH > 0), as temperature increases, K increases.

Express equilibrium constants in terms of thermodynamic activities.
Explain why the chemical equilibrium constant is dimensionless.
Explain why the equilibrium constant is independent of pressure.
Calculate heat of reaction at 298 K from heats of formation.
Calculate how the equilibrium constant changes with temperature.
Calculate the standard Gibbs free energy change for a reaction at 298 K, and its equilibrium constant, from Gibbs free energies of formation.
Calculate equilibrium conversions.
Explain why pressures must be in bar in equilibrium calculations.
Describe how equilibrium constants change with temperature for endothermic and exothermic reactions.
Calculate equilibrium mole fraction for ideal gases and non-ideal gases.
Predict how pressure changes will shift equilibrium conversion for a gas-phase reaction with a mole change.
Predict how an addition of an inert will affect equilibrium conversion.

Prepared by John L. Falconer, Department of Chemical and Biological Engineering, University of Colorado Boulder

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