Chemical Equilibrium

Stating that a chemical reaction is at equilibrium implies that both the forward and reverse reaction rates are equal. One way to describe the equilibrium position of the reaction is to give the equilibrium concentrations of the reactants and products; the equilibrium constant expression relates these concentrations at equilibrium at a given temperature to a numerical constant, K.

This module simulates chemical equilibrium using the reaction of aqueous Fe³⁺ and SCN^- to form iron thiocyanate. The concentration of both the reactants and products can be manipulated. The concentrations of the three solution species are plotted as a function of time as they move toward equilibrium. Upon equilibration, value of the reaction quotient following equilibrium is calculated.

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INSTRUCTIONS

1. Adjust the concentrations of Fe³⁺ and SCN^- from 0 to 0.001 M using the appropriate vertical scroll bars.
2. Click on the Equilibrate button to view the results at equilibrium. Note that both initial concentration values must be greater than zero. The program will beep and no plot will be drawn if either value is zero.
3. Observe the plot of the reagent and product concentrations vs. the time the reaction has proceeded to equilibrium. In addition, the near equilibrium concentrations are given in the lower right-hand corner; the equilibrium constant is calculated based on these concentration values.
4. Review or readjust the initial concentration values and repeat as desired.