# Vapor Density of Gas

on . Posted in Classical Mechanics

Vapor density is a measure of the density of a gas or vapor compared to the density of a reference gas.  The reference gas is typically air, which is assigned a vapor density of 1.  The vapor density of a gas is useful for various purposes, including determining whether a gas will rise or sink in air.  Gases with a vapor density less than 1 are lighter than air and will tend to rise, while gases with a vapor density greater than 1 are heavier than air and will tend to sink.

### Vapor density example

• Hydrogen gas (H2) has a molar mass of approximately 2 grams per mole, so its vapor density is 1 (2/2).
• Carbon dioxide gas (CO2) has a molar mass of approximately 44 grams per mole, so its vapor density is 22 (44/2), indicating that it is much heavier than air.

### Vapor Density of Gas formula

$$G_{vd} = G \;/\; H$$     (Vapor Density of Gas)

$$G = G_{vd} \; H$$

$$H = G \;/\; G_{vd}$$

Symbol English Metric
$$\large{ G_{vd} }$$ = vapor density of gas $$lbm \;/\; ft^3$$  $$kg \;/\; m^3$$
$$\large{ G }$$ = gas density $$lbm \;/\; ft^3$$  $$kg \;/\; m^3$$
$$\large{ H }$$ = hydrogen density $$lbm \;/\; ft^3$$  $$kg \;/\; m^3$$

Tags: Gas Density Vapor