A sample of gaseous PCl 5 was introduced into an evacuated flask so that the pre

Question

A sample of gaseous PCl5 was introduced into an evacuated flask so that the pressure of pure PCl5 would be 0.46 atm at 427 K. However, PCl5 decomposes to gaseous PCl3 and Cl2, and the actual pressure in the flask was found to be 0.74 atm. Calculate Kp for the decomposition reaction below at 427 K.

A sample of gaseous PCl5 was introduced into an evacuated flask so that the pressure of pure PCl5 would be 0.46 atm at 427 K. However, PCl5 decomposes to gaseous PCl3 and Cl2, and the actual pressure in the flask was found to be 0.74 atm. Calculate Kp for the decomposition reaction below at 427 K. PCl5(g) PCl3(g) + Cl2(g) Also calculate K at this temperature.

Explanation / Answer

PCl5 <---> PCl3 + Cl2

I 0.46 0 0

C - x x x

E 0.46-x x x

The final pressures add up to 0.74.

(0.46-x) + 2x = 0.74

0.46 + x = 0.74

x = 0.28 atm

Kp = P(PCl3) * P(Cl2) / P(PCl5)

= (0.28)(0.28) / (0.46-0.28)

= (0.28)(0.28)/(0.18)

= 0.44

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