Problem: Ammonium iodide can dissociate to produce HI and ammonia, NH4I(s) ⇌ NH3(g) + HI(g). At 300 °C, Kp = 0.42. If 250. g of ammonium iodide is placed into a 3.00 L flask and heated to 300 °C, what is the partial pressure of ammonia at equilibrium?a. 0.84 atm b. 0.21 atmc. 0.42 atmd. 0.65 atme. 0.18 atm

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We’re being asked to determine the partial pressure of Ammonia when 250 g of NH4I is placed in a 3 L flasked heated up to 300°C


 NH4I(s)  NH3(g) + HI(g)


Recall that the equilibrium constant is the ratio of the products and reactants.  We use Kp when dealing with pressure and Kc when dealing with concentration:


Kp=PproductsPreactants     Kc=[products][reactants]


Note that solid and liquid compounds are ignored in the equilibrium expression.

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Problem Details

Ammonium iodide can dissociate to produce HI and ammonia, NH4I(s) ⇌ NH3(g) + HI(g). At 300 °C, Kp = 0.42. If 250. g of ammonium iodide is placed into a 3.00 L flask and heated to 300 °C, what is the partial pressure of ammonia at equilibrium?

a. 0.84 atm 

b. 0.21 atm

c. 0.42 atm

d. 0.65 atm

e. 0.18 atm