I need to determine the equilibrium constant for this estiferication process thr

Question

I need to determine the equilibrium constant for this estiferication process through forward and reverse reaction data. The moles of acid present at equilibrium were determined from titration with standard NaOH solution; however, the presence of HCl catalyst complicates the calculation, because the moles of acid present is equal to the combined moles of HCl and Acetic Acid. Essentially we subtract the moles of HCl from the moles of acid present (moles of OH- titrated) to obtain moles of acetic acid at equilibrium. Then we determine the difference of moles of acetic acid from the initial amount, and use stoichiometric ratios (1:1) to determine the equilibrium concentrations of the other reacion components. The equilibrium constant then equals the ratio of product concentrations to reactant concentrations. Molar amounts may be used instead of concentration because the volume terms will cancel.

For some reason I am obtaining K fwd = ~21 and K rev = ~2, though K fwd and K rev both should approximately equal 4. If I do the redo calculations ignoring affects of HCl on the titration, all K's approximately equal 4, but I am certain HCl was added to the reaction mixture.

QUESTION: Can you explain this inconsistency or illustrate an error in my calculations?

Reaction:

CH3COOH + CH3CH2OH <<-- HCl -->> CH3COOCH2CH3 + H2O

Acetic Acid + Ethanol <<-- HCl -->> Ethyl Acetate + Water

Table 1: Concentrations & Densities Acid Concentration, M Density, g · mL¹ Formula Molar Mass , g mol¹ Hydrochloric Acid 3.5051 1.050 HCl 36.458 Ethanol - 0.7880 C2H6O 46.068 Ethyl Acetate - 0.902 C4H8O2 88.104 Glacial Acetic Acid - 1.049 CHCOOH 60.052 Sodium Hydroxide 0.7060 - NaOH 39.998 Water (pure) - 1.00 H2O 18.016

Explanation / Answer

Remember:

At equilbrium :

the reaction rate of the forward reaction is equal to the reaction rate of the backward reaction, and not the rate constant.

so why you want them to be equal.

simply calculate Keq = [Products] / [Reactants]

K backward will not be equal to K forward.

Hope its clear now!!

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