Answer:
Mass  = 1600 g
Explanation:
Given data:
Number of moles of argon = 150.0 mol
Initial temperature = 25°C (25+273= 298 K)
Initial pressure = 7.65 MPa
Final pressure = 2.0 MPa
Final temperature = 19°C (19+273 = 292 k)
Final number of moles = ?
Solution:
According to ideal gas law,
when volume is remain constant then the pressure of gas is directly proportional to the number of moles and temperature.
Mathematical expression,
Pâ/nâTâ Â = Â Â Pâ/nâTâ Â .........(1)
Pâ = Initial pressure
nâ = Initial number of moles
Tâ = Initial temperature Â
Pâ = Final pressure
nâ = Final number of moles
Tâ = Final temperature
Now we will put the values in equation 1.
Pâ/nâTâ Â = Â Â Pâ/nâTâ Â
7.65 MPa / 150 molĂ298 K = 2.0 MPa / nâĂ 292K
nâ = Â 2.0 MPa Ă150molĂ298 K/ 292K Ă 7.65 MPa
nâ = Â 89400 mol / 2233.8
nâ = 40.0 mol
Mass of argon remain:
Mass = number of moles Ă molar mass
Mass = 40.0 mol Ă 40.0 g/mol
Mass  = 1600 g
Initial mass:
Initial mass = number of moles Ă molar mass
Initial mass = 150.0 mol Ă 40.0 g/mol
Initial mass = 6000 g