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Ammonium hydrogen sulfide dissociates into ammonia gas and hydrogen sulfide gas. If we start with a sample of pure NH_{4}HS(s) at 25 ^{o}C, the total pressure of the gases is 0.658 atm when equilibrium is established. Write an equation for the dissociation reaction and determine the value of K_{p}
Set up a table:








Initial 




Change 




Equilibrium 



In this case x represents the partial pressure of the gases in the container and the total pressure in the container is equal to the sum of the partial pressures (Dalton's Law of Partial Pressures). Thus, 0.658 atm = x + x = 2x, or x = 0.329 atm.
Now, K_{p} = (x)(x) = x^{2} = (0.329)^{2} = 0.108.