Equilibrium Exp
Equilibrium
In your text (Chang, 6th Ed) : Ch. 15 Chemical Equilibrium, esp. Section 15.3
Purpose: The Law of Mass Action will be examined via a series of samples using the same reaction, but different stating concentrations. The equilibrium constant, K, for each reaction will be calculated, demonstrating that K for a given reaction at a fixed temperature is a constant, independent of starting concentrations.
Background: For a general reaction aA + bB ↔ cC + dD, the Law of Mass Action (formulated by Guldberg and Waage, 1864) in terms of concentration is:
[pic] = K (Eqn. 1)
For gases, K can also be stated in terms of partial pressures, and hence is labeled as Kp: [pic] = Kp (Eqn. 2)
In either case, the terms must be referenced to standard states, 1 M or 1 atm, so the numbers in the equations are unitless, and the K’s are unitless. For a given reaction, different initial concentrations will yield differing final concentrations, but K, the ratio of products over reactants, all terms raised to their stoichiometric coefficients, is a constant at a fixed temperature. (K is a function of temperature.)
In this experiment, five samples of different initial concentrations will be prepared for the reaction:
Fe+3(aq) + SCN-(aq) ↔ FeSCN+2(aq) (Eqn. 3)
Equilibrium calculations are simplified by using an ICE (Initial-Change-Equilibrium) table. Since this reaction is run in aqueous solution, the K calculated will be Kc (K in terms of concentration), and all concentrations must be expressed in terms of M, or moles/liter, then reference to the standard state of 1M.
To calculate the equilibrium concentrations and K, the ICE table is:
Fe+3(aq) + SCN-(aq) ↔ FeSCN+2(aq)
I Co Co’ 0
C -x -x +x
E Co - x Co’- x x
where
Co = initial concentration of Fe+3(aq) {Co mol/L ( 1 mol/L = Co}
Co’
In your text (Chang, 6th Ed) : Ch. 15 Chemical Equilibrium, esp. Section 15.3
Purpose: The Law of Mass Action will be examined via a series of samples using the same reaction, but different stating concentrations. The equilibrium constant, K, for each reaction will be calculated, demonstrating that K for a given reaction at a fixed temperature is a constant, independent of starting concentrations.
Background: For a general reaction aA + bB ↔ cC + dD, the Law of Mass Action (formulated by Guldberg and Waage, 1864) in terms of concentration is:
[pic] = K (Eqn. 1)
For gases, K can also be stated in terms of partial pressures, and hence is labeled as Kp: [pic] = Kp (Eqn. 2)
In either case, the terms must be referenced to standard states, 1 M or 1 atm, so the numbers in the equations are unitless, and the K’s are unitless. For a given reaction, different initial concentrations will yield differing final concentrations, but K, the ratio of products over reactants, all terms raised to their stoichiometric coefficients, is a constant at a fixed temperature. (K is a function of temperature.)
In this experiment, five samples of different initial concentrations will be prepared for the reaction:
Fe+3(aq) + SCN-(aq) ↔ FeSCN+2(aq) (Eqn. 3)
Equilibrium calculations are simplified by using an ICE (Initial-Change-Equilibrium) table. Since this reaction is run in aqueous solution, the K calculated will be Kc (K in terms of concentration), and all concentrations must be expressed in terms of M, or moles/liter, then reference to the standard state of 1M.
To calculate the equilibrium concentrations and K, the ICE table is:
Fe+3(aq) + SCN-(aq) ↔ FeSCN+2(aq)
I Co Co’ 0
C -x -x +x
E Co - x Co’- x x
where
Co = initial concentration of Fe+3(aq) {Co mol/L ( 1 mol/L = Co}
Co’