Question

Nitrogen monoxide reacts with chlorine gas according to the reaction:

2NO (g) + Cl2 (g) ⇔ 2NOCl (g) Kp = 0.27 at 700 K

A reaction mixture initially contains equal partial pressures of NO and Cl2 . At equilibrium, the partial pressure of NOCl is 115 torr. What were the initial pressures of NO and Cl2?

Answer 1

NOCl at equilibrium is 115/760 = approximately 0.15 atm but you can use a more accurate number.

......2NO + Cl2 --> 2NOCl
I......P.....P........0
C.......
E....................0.15

Here is how you figure the rest.
Do the C line next. We know equilibium NOCl is 0.15. Since it was 0 to start, then change MUST have been +0.15. Then C for NO must be -0.15 and for Cl2 must be -0.15/2. Then E for NO must be P-0.15 and E for Cl2 must be -0.15/2.
Substitute these values into Kp expression and solve for P. The answer will be in atm