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Question Video: Writing the Equilibrium Constant for Concentration Equation for the Hydrolysis of an Ester Chemistry

For the following equilibrium showing the hydrolysis of an ester, find the correct equation for 𝐾_c: CH₃COOCH₃ + H₂O ⇌ CH₃COOH + CH₃OH

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Video Transcript

For the following equilibrium showing the hydrolysis of an ester, find the correct equation for 𝐾 𝑐. CH3COOCH3 plus H2O is in equilibrium with CH3COOH plus CH3OH.

In this question, we need to determine the 𝐾 𝑐 for the hydrolysis of the ester methyl acetate, which produces acetic acid and methanol when reacted with water. 𝐾 𝑐 is the equilibrium constant for concentration. The equilibrium constant for concentration expresses a value related to the ratio between the concentrations of the reactants and products at equilibrium.

Let’s consider a generic equilibrium reaction equation. In this equation, the lowercase letters represent stoichiometric coefficients and the uppercase letters represent chemical formulas. For the generic reaction equation, we can write the following equation for the equilibrium constant for concentration. 𝐾 𝑐 equals the concentration of the products raised to their stoichiometric coefficients divided by the concentration of the reactants raised to their stoichiometric coefficients.

It’s worth noting that species in the solid phase and pure water when used as a solvent do not appear in the equilibrium constant for concentration equation. All of the species involved in the given reaction are liquids. In addition, water in this reaction is a reactant, not just a solvent. So all of the species involved in the reaction should appear in the equilibrium constant for concentration equation.

With this in mind, we can follow the generic equation to write the correct equation for 𝐾 𝑐 for this reaction. We find that to determine the equilibrium constant for concentration for this reaction, we need to multiply the concentration of acetic acid by the concentration of methanol then divide by the concentration of methyl acetate and the concentration of water.

In conclusion, the correct equation for 𝐾 𝑐 is 𝐾 𝑐 equals the concentration of CH3COOH times the concentration of CH3OH divided by the concentration of CH3COOCH3 times the concentration of H2O.

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