# Van der waals gas

1. Dec 10, 2006

### ja87

1. The problem statement, all variables and given/known data
i must use van der waals gas equation to plot a pressure against volume graph for H2O. i must do 3 plots on one graph, one of the critical temperature given a point of inflection, one where temperature is less than the critical temperature giving a large dip in the graph, and one where T>critical temperature and hence gives a a curve where dp/dv is never =0.

2. Relevant equations
i have the van der waals equation :(p+a(1/v)^2)*(v-b) = n*R*T
and have rearranged to make p=-(-a(1/v)^2*v+a(1/v)^2*b+n*R*T)/(-v+b)
i also have a=0.5507, b=3.04*10^-5, R=8.314, n=1

3. The attempt at a solution

i have tried to plot a p(v) graph with these values in this equation (using Maple) using small, large and negative values for T and all i get is a graph that looks like a 1/x graph, i cannot get the desired dip for when T<critical temperature. am i using the wrong equation or are my numbers wrong.