Relative gas density is a comparison of the relative molecular or molar mass of one gas with that of another gas. As a rule, it is determined in relation to the lightest gas - hydrogen. Also, gases are often compared with air.
In order to show which gas is selected for comparison, an index is added in front of the symbol of relative density of the test, and the name itself is written in brackets. For example, DH2 (SO2). This means that the density of sulfur oxide was calculated from hydrogen. It reads as "the density of sulfur oxide in hydrogen."
In order to calculate the gas density by hydrogen, it is necessary to determine the molar masses of the test gas and hydrogen using a periodic table. If it is chlorine and hydrogen, then the indicators will look like this: M (Cl2) = 71 g / mol and M (H2) = 2 g / mol. If the density of hydrogen is divided by the density of chlorine (71: 2), the result is 35.5. That is, chlorine is 35.5 times heavier than hydrogen.
The relative density of the gas does not depend on external conditions. This is explained by the universal laws of the state of gases, which boil down to the fact that a change in temperature and pressure does not lead to a change in their volume. With any changes in these indicators, measurements are made in exactly the same way.
To determine the density of gas empirically, you need a bulb where it can be placed. The gas flask must be weighed twice: the first time - having pumped all the air out of it; the second - filling it with the test gas. It is also necessary to measure the volume of the flask in advance.
First you need to calculate the mass difference and divide it by the value of the volume of the flask. As a result, the gas density will be obtained under given conditions. Using the equation of state, you can calculate the desired indicator under normal or ideal conditions.
You can find out the density of some gases from the pivot table, which has ready-made information. If the gas is listed in the table, then you can take this information without any additional calculations and the use of formulas. For example, the density of water vapor can be found on the table of water properties (Rivkina S.L. Handbook, etc.), its electronic counterpart, or using programs like WaterSteamPro and others.
However, in different liquids, equilibrium with steam occurs at different densities of the latter. This is due to the difference in the forces of intermolecular interaction. The higher it is, the faster equilibrium will come (for example, mercury). In volatile liquids (such as ether), equilibrium can only occur at a significant vapor density.
The density of various natural gases varies from 0.72 to 2.00 kg / m3 and higher, relative - from 0.6 to 1.5 and higher. The highest density is for gases with the highest content of heavy hydrocarbons H2S, CO2 and N2, the lowest is for dry methane.
The properties of natural gas are determined by its composition, temperature, pressure and density. The last indicator is determined by laboratory means. It depends on all of the above. You can determine its density by different methods. The most accurate - weighing on accurate scales in a thin-walled glass bottle.
Air density is greater than that of natural gases. In practice, this ratio is taken as 0.6: 1. Static air pressure decreases faster compared to gas. At pressures up to 100 MPa, the density of natural gas can exceed 0.35 g / cm3.
It has been established that an increase in the density of natural gas can be accompanied by an increase in the temperature of hydrate formation. Low-density natural gas forms hydrates at a higher temperature compared to high-density gases.
In the gas industry, density meters are just beginning to be used and there are still many questions that are related to the features of their operation and verification.