Question

Two moles of a gas are confined to five
litre flask and 27°C. Calculate the
pressure using van der Waals equation to
the nearest integer. For ammonia a =
6.25 atm lita mol-2 and b = 0.037 lit mol-1​

Answer 1

Given : Number of moles, n = 2, Volume, V = 5L, Temperature, T = 27°C = 27 + 273 = 300K

• Van der Waals constant a and b are 6.25 atm lita mol-2 and 0.037 lit mol-1 respectively.

To find : Pressure using van der Waals equation

Solution : We know that the van der Waals equation is given by the formula :

$[ P + an {}^{2} /V {}^{2} ]×[ V - nb ] = nRT$

• [ P + 6.25×2×2/5×5 ]×[ 5 - 2×0.037 ] = 2×8.314×300

(P + 1)×(5 - 0.074) = 4988.4

(P + 1)×4.926 = 4988.4

P + 1 = 1012.67

• P = 1011.67

Hence, Pressure is 1011.67