Let us assume that initially, 100 moles of CO2 are present.
2 moles of CO2 decompose to form 2 moles of CO and 1 mole of O2.
100−2=98 moles of CO2 remains.
The mole fraction of CO2 at equilibrium =98100=0.98
The partial pressure of CO2 at equilibrium =0.98×1atm=0.98atm.
The mole fraction of CO at equilibrium =2100=0.02
The partial pressure of CO at equilibrium =0.02×1atm=0.02atm.
The mole fraction of O2 at equilibrium =1100=0.01
The partial pressure of O2 at equilibrium =0.01×1atm=0.01atm.
KP=P2COPO2P2CO2
KP=(0.02atm)2×0.01atm(0.98atm)2
KP=4.12×10−6atm