A vessel at 1000 K contains CO2 with a pressure of 0.5 atm. Some of the CO2 is converted into CO on the addition of graphite. If the total pressure at equilibrium is 0.8 atm, the value of KP is

CO2(g)  +  C (s)   ⇌  2CO (g)Initial          0.5 atmAt equilibrium   (0.5 - p)      2p atmThis is a case of heterogeneous equilibrium.C(s) being solid is not considered.Total pressure of CO2 and CO gases.PCO2  +  PCO  =  Ptotal 0.5 - (p + 2p) = 0.8,  p = 0.3 atm∴      PCO2  =  0.5 - 0.3 = 0.2 atmpCO = 2p = 0.6 atmKP = pCO2pCO20.6 × 0.60.2 = 1.8 atm