Question

# A 20-ft3 tank contains natural gas with the composition given below. After removing 200 SCF from...

A 20-ft3 tank contains natural gas with the composition given below. After removing 200 SCF from the tank, the pressure and temperature drop to 1800 psia and 80oF. Determine the how many moles of gas were in the tank originally.

 Component Mole % C1 89.50 C2 4.50 C3 3.50 iC4 0.70 nC4 0.60 iC5 0.40 nC5 0.20 C6 0.10 C7+ 0.50 MC7+= 110 ϒ C7+= 0.75

We know that Standard Cubic Foot = one cubic foot of gas at 21°C or 70°F and 101.35 kilopascals pressure or 14.7 psai = 760 mmHg

Moles of gas = 1.2 moles at SCF OR 0.002 lbs moles

Let initial moles = x

so decrease in moles = x-0.002

So new gas equation will be

PV = nRT

R = gas constant = 998.9 ft3 mmHg K−1 lb-mol−1

P = 1800psai = 93086.8 mmHg

V = 20 ft^3

n = x-0.002

T = 800F = 299.8 K

x-0.002 = 93086.8 X 20 / 998.9 X 299.8 = 6.216

x = 6.218 lb moles = 2819 moles

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