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Equilibrium constant

by fk378
Tags: constant, equilibrium
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Mar9-08, 10:21 PM
P: 367
1. The problem statement, all variables and given/known data
The total pressure of gases in equilibrium with solid sodium hydrogen carbonate at 110.0 degrees C is 1.648 atm, corresponding to the reaction

2NaHCO3(s) <--> Na2CO3(s) + H2O(g) + CO2(g)

a) Calculate the value of the equilibrium constant at 110.0 degrees C.

3. The attempt at a solution
I don't know how to begin this because I don't know how to find the initial partial pressure of sodium hydrogen carbonate. How am I supposed to use P total at equilibrium in this problem?
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Mar10-08, 02:00 AM
P: 44
The solid sodium bicarbonate has negligible vapor pressure at 110 degrees C. We usually treat solids as constants, which we then divide out of the equilibrium constant; the only terms you should be left with in your expression for K are from gaseous water and gaseous carbon dioxide.

This approach for dealing with solids holds true in general, unless the equilibrium being studied occurs in a solid solution (e.g., molten rock.)

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