From the ideal gas law pv=nRT , n is therefore PV/RT R is the R is gas constant =62.364 torr/mol/k P=500torr V=4.00l T=500+273=773k n={(500 torr x 4.00l)/(62.364 x773k)}=0.041moles the number of molecules=moles x avorgadro costant that is 6.022x10^23) 6.022 x 10^23) x0.041=2.469 x10^22molecules
