Need help with all parts please!

4) For many real gases the values for the a and b coefficients needed for use in the van der Waals equation ar e not known. However, if the location of the critical point for a gas is known, values for a and b can be estimated frr m the critical pressure and temperature of the gas, using the relationships pc=27b2aTc=27Rb8a a) Starting with the relationships in 4.1, find expressions for the van der Waals a and b coefficien ts in terms of pc,Tc, and/or other constants. b) The critical constants for ammonia (NH3) are pc=111.3atm,Tc=405.5K. Based on this information and your answers in part a, find the values for the van der Waals coefficients a and b for ammonia. Give the values in units of L2atm/mol2 (for a ) and L/mol (for b). If you have done this problem correctly you should get those reported for ammonia (a=4.169L2atm/mol2,b=0.0371L/mol. c) Since Vm,c=3b it would seem much easier to find the van der Waals b coefficient from t is expression than from the relationships in 4.1 Wht is this not done