- #1
Saptarshi Sarkar
- 99
- 13
- Homework Statement
- A non-ideal gas is described by the VdW law
##(P+an^2)(1-nb) = nkT##
where a,b and k are positive constants, n is the density of particles, P the pressure, and T the temperature.
How will n change (increase or decrease) if we
1) Hold P and increase T
2) Hold T and increase P
- Relevant Equations
- ##(P+an^2)(1-nb) = nkT##
My attempt
I calculated the partial derivatives of n wrt P and T. They are given below.
##\frac {\partial n}{\partial P} = \frac{nb -1}{\left(2an-Pb-3abn^2-kT\right )}##
##\frac {\partial n}{\partial T}= \frac {nk}{\left(2an-Pb-3abn^2-kT \right ) }##
I know that if the partial derivative is positive, n should increase with the increase in the independent variable and if the partial derivative is negative, n should decrease with the increase in the independent variable. But, I am not sure how to determine if the above partial derivatives are positive or negative.
I calculated the partial derivatives of n wrt P and T. They are given below.
##\frac {\partial n}{\partial P} = \frac{nb -1}{\left(2an-Pb-3abn^2-kT\right )}##
##\frac {\partial n}{\partial T}= \frac {nk}{\left(2an-Pb-3abn^2-kT \right ) }##
I know that if the partial derivative is positive, n should increase with the increase in the independent variable and if the partial derivative is negative, n should decrease with the increase in the independent variable. But, I am not sure how to determine if the above partial derivatives are positive or negative.
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