AP CHEMISTRY GAS LAWS

Question

If 3.21 Moles of ammonia gas occupy 5.22 L at 50 degrees C, calculate the pressure of the gas using the ideal gas equation and by using the van der Waals equation. Compare each value to the actual measured pressure of 15.4 atm under these conditions, and comment upon the values.

For ammonia under these conditions, a = 4.17 atm L² mol^-2 and b = 0.0371 L mol^-1

Answer 1

Write van der Waals' Equation as (P + n²a/V²)(V − nb) = nRT.

Place values given to obtain [P + (3.21² • 4.17)/5.22²] atm times [5.22 L − (3.21 mol)(0.0371 L/mol)] equals [3.21 mol][0.0821 (L• atm)/(mol • K)][273.15 + 50]K which simplifies to P = 15.11880195 atmospheres.

Write the Ideal Gas Equation as PV = nRT.

Place supplied values to to obtain P(5.22 L) = [3.21 mol][0.0821 (L• atm)/(mol • K)][273.15 + 50]K. This in turn reduces to P = 16.31480348 atmospheres which is further from the actual measured pressure of 15.4 atmospheres than is the van der Waals solution of 15.11880195 atmospheres.