Methane is stored under pressure in a 1 m³ tank. The pressure in the tank is 20 bar and the temperature is 25 °C.

a). Calculate the compressibility factor of methane in the tank from the virial equation truncated after the second term. 

b). What is the amount (moles) of methane in the tank? 

c). You want to store twice as much methane in the tank at the same temperature. What will be the pressure in the tank? 

d). Is it appropriate to use the virial equation for this problem? 

Explain. At 25 °C the second virial coefficient of methane is −4.22 × 10⁻⁵ m³/mol.