# Vander waal coefficients ?

1. Apr 7, 2008

### mkbh_10

Calculate critical temp. for a gas obeying vander waal eqn of state . Give a = .00874 atm (cm)^6 & b = .0023 (cm)^3 for 1 (cm)^3 of gas at STP .

unit of a is N (m)^4 (mol)^-2 , how do i get this mol term ?

(cm)^6 = (10)^-12 (m)^6 , pressure at STP is 1 atm = 1.013*(10)^5 N/m(sqr) ,

combining these two this equals

1.013 (10)^-7 N (m)^4 , to get the per mol term , i use the eqn of state PV=nRT where

p = 1 atm , V= 22.4 ltrs = 22.4 *(10)^-3 (m)^3 , R= 8.31 J/k/mol T = 273 K

I am stuck after this , is the conversion of volume correct ?