2NO(g) + O2(g) = 2NO2

Question

If there are .02 moles of O2, .04 moles of NO, and .96 moles of 2NO2, calculate Kp if the total pressure is .2 atm.

Answer 1

The partial pressures are:
(0.02/1.02) * 0.2 = 0.00392 atm O2
(0.04/1.02) * 0.2 = 0.00784 atm NO
(0.96/1.02) * 0.2 = 0.1882 atm NO2

Now calculate the appropriate Kp value.

Kp = PCO2^2/[PNO^2*PO2]

This assumes that mixture is in chemical equlibrium. This is not always the case.