Oxygen has the chemical formula O2 and the molecular mass of 32 g/mole. Liquid oxygen has medicine and scientific applications and is a convenient form for storing this compound. The liquid compound is about 1,000 times denser than the gaseous oxygen. The volume of the gaseous oxygen depends upon temperature, pressure as well as the mass of the compound. As an example, calculate the volume of the gaseous oxygen at 20 Celsius and the pressure of one atmosphere (atm) that is obtained from evaporation of 70 liters (L) of liquid oxygen.
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Multiply the volume (in Liters) of the liquid oxygen by 1,000 to convert it to milliliters (ml). In our example 70 L will be converted to 70,000 ml.

Multiply the volume of the liquid oxygen by its density, 1.14 g/ml, to calculate the mass of the compound. In our example, the mass of oxygen is 70,000 ml x 1.14 g/ml or 79,800 g.

Divide the mass of oxygen by its molecular mass to calculate the number of moles. In our example, the oxygen amount is 79,800 g / 32 g/mole = 2,493.75 moles.

Convert temperature in Celsius to Kelvin (K) by adding the value "273.15." In this example, temperature is 20 + 273.15 = 293.15 K.

Multiply the pressure in atm by the factor "101,325" to convert the pressure to the SI unit Pascal (Pa).
In our example, Pressure = 101,325 x 1 atm = 101,325 Pa. 
Round the molar gas constant R to the fourth digit to obtain 8.3145 J/mole x K.
Note that the constant is given in the International System of Units (SI). "J" means Joule, a unit of energy. 
Calculate the volume (in cubic meters) of gaseous oxygen using the ideal gas law: multiply the amount of oxygen (in moles) by temperature and the molar gas constant followed by dividing the product by pressure. In our example,
Volume = 2493.75 (mole) x 8.3145 (J/mole x K) x 293.15(K) / 101,325 (Pa) = 59.99 cubic meters or 59,990 L.
References
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