How to Find Grams Using the Van der Waals Equation

The inconstant, unfixed nature of gases has historically made them a challenge for chemists to measure and evaluate. The Ideal Gas Law was developed to mathematically explain the behavior of gases. Johannes van der Waals then developed an improved version of the law. The equation is P + (a^2/V^2)](V - b) = nRT, where P equals pressure, V equals volume, n equals the number of moles, T is temperature, R is the ideal gas constant and a and b are constants that vary according to the experiment. You can rework the equation to solve for mass in grams.

Instructions

1. • 1

     Isolate n, the number of moles, which can thereby be converted to mass in grams, by dividing each side by RT, yielding the equation [P + (a^2/V^2)](V - b)]/RT = n.

   • 2

     Solve for n based on the values in your given experiment or problem.

   • 3

     Convert n (again, the number of moles) to grams, using the formula (grams/moles)/(molar mass in grams)/(one mole). The specific values will depend on the gas whose properties you're trying to solve for.

   • 4

     Multiply each side by n to isolate the variable g, in grams, and perform the calculations to find the number.