1. A 3.00-L flask is filled with gaseous ammonia, NH3. The gas pressure measured

Question

1. A 3.00-L flask is filled with gaseous ammonia, NH3. The gas pressure measured at 18.0 C is 1.95 atm . Assuming ideal gas behavior, how many grams of ammonia are in the flask? Express your answer to three significant figures and include the appropriate units.

2. If 1.00 mol of argon is placed in a 0.500-L container at 28.0 C , what is the difference between the ideal pressure (as predicted by the ideal gas law) and the real pressure (as predicted by the van der Waals equation)? For argon, a=1.345(L2atm)/mol2 and b=0.03219L/mol. Express your answer to two significant figures and include the appropriate units.

Explanation / Answer

1) V=3 L T= 18 C = 291 K and P = 1.95 atm Molar mass of NH3 = 17g/mol

Thus using the ideal gas equation PV = nRT

1.95atm x 3.00L = (x g/17g/mol) (0.0821L.atm/mol.K x 291K)

Thus mass = x = 0.416g

2) a) Assuming ideal behaviour PV = nRT

Given P = ? V = 0.5 L ,T = 28 C =301 K and n= 1.00

P = nRT/V

= 1.00x 0.0821 x 301 /0.5

=49.42 atm

b) real behaviour

[P+ an2/V2][ V - nb] = nRT

Given a= 1.345L2.atm/mol2  and b = 0.03219 L/mol

Thus

[ P + (1.345)2/(0.5)2] [ 0.5 - 0.03219] = 0.0821 x301

Solving for P

P= 45.59atm

The difference betwween real pressure and ideal pressure = 49.42 -45.59

=3.83 atm

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