By using Ideal gas equation, PV=nRT ⇒0.4atm×20L=nCO2×R×400K ⇒nCO2=
0.2
R
mole ⇒ Initial moles of CO2 After reaching the Equilibrium, SrCO3(s)⇌SrO(s)+CO2(g) All pressure will be because of CO2 only as it is the gaseous substance. ∴KP=PCO2=1.6atm P2V2=nRT ⇒1.6atm×V2=
0.2
R
×R×400 ⇒V2=5L Thus when the pressure of CO2 will be maximum i.e. 1.6atm the volume will be 5L.