a.) You have a 1.0-L flask filled with phosphorous pentachloride (PCl5) at a hig

Question

a.) You have a 1.0-L flask filled with phosphorous pentachloride (PCl5) at a high enough temperature such that it is entirely in gaseous form. You remember that PCl5 can decompose into chlorine gas (Cl2) and phosphorous trichloride gas (PCl3) in an equilibrium reaction. You start with one atm of PCl5 in your flask. After equilibrium is achieved at constant temperature, you notice that the new pressure inside the flask is fifty percent higher than the initial pressure. Determine the value of the equilibrium constant, Kp, for the reaction.

b.) you are having lunch with a friend, who is also studying the same reaction in a 1.0-L flask at the same temperature. She has combined one atm of each of the three gases in a flask, and is now wondering what will happen. Based on your own observations of this reaction, do you predict that the pressure in her flask will go up, go down, or remain the same? Explain in detail.

Explanation / Answer

PCl5 <------------------> PCl3 + Cl2

1 atm                                 0            0

1 - x                                   x             x

here after equilibrium the pressure inside flask increases 50% higher

so

1- x + x + x = 1.5

x = 0.5

PCl2 = PPCl3 = 0.5 atm

P PCl5 = 1 - x = 0.5 atm

Kp = PCl2 x PPCl3 / PPCl5

      = 0.5^2 / 0.5

      = 0.5

Kp = 0.5

2 )

each one has 1 atm pressure.

in the mixture equilibrium attains . reactants pressure decreases and product pressure decreases, but over all pressure of the container remains the same

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