Question

How different is the measured volume from the volume if it had been obtained under STP? Is the difference greater than an assumed measurement error of 5%? If not, why should we go to all this trouble to make this calculation?

Answer 1

STP is commonly used to define standard conditions for temperature and pressure which is important for the measurements and documentation of chemical and physical processes:

1. STP - Standard Temperature and Pressure - is defined by IUPAC (International Union of Pure and Applied Chemistry) as air at 0^oC (273.15 K, 32 ^oF) and 10⁵ pascals (1 bar).

At these conditions, the volume of 1 mol of a gas is 22.4136 liters.

• NTP - Normal Temperature and Pressure - is defined as air at 20^oC (293.15 K, 68^oF) and 1 atm (101.325 kN/m², 101.325 kPa, 14.7 psia, 0 psig, 29.92 in Hg, 407 in H₂O, 760 torr). Density 1.204 kg/m³ (0.075 pounds per cubic foot)
  • At these conditions, the volume of 1 mol of a gas is 24.0548 liters.

hence we can see the difference temperature affects the molar volume to any substace.

In above we can see that the difference of STP and NTP on the molar volume is of 2L.

If we see in terms of 5%, the 5% of 22.4L is 1.12L and our result shows more than 5% is the difference we can observe on measured volume from the volume if it had been obtained under STP.