First Principles - Sustainable Design: The Science of Sustainability and Green Engineering - page 63

ideal gas law:

ρ = p ( RT ) − 1

(2.13)

where
p

= gas pressure

=

R specific gas constant

=

T absolute temperature

The specific gas constant must be known to calculate gas density. For example,
the R value for air is 287 J kg − 1 K − 1 . The specific gas constant for methane
( R CH4 )is518Jkg − 1 K − 1 .
Density is a very important fluid property in green design and operations. For
example, a first responder must know the density of substances in an emergency
situation. If a substance is burning, whether it is of greater or lesser density
than water will be one of the factors in determining how to extinguish the fire.
If the substance is less dense than water, the water will probably settle below
the layer of water, making water a poor choice for fighting the fire. So any
flammable substance whose density is less than that of water (see Table 2.2), such

Table 2.2 Densities of Some Important Environmental Fluids

Density (kg m − 3 )at20 ◦ C

Fluid (unless otherwise noted)

Air at standard temperature and pressure
(STP) = 0 ◦ C and 101.3 N m − 2

1.29

Air at 21 ◦ C 1.20

Ammonia 602

Gasoline 700

Diethyl ether 740

Ethanol 790

Acetone 791

Kerosene 820

Turpentine 870

Benzene 879

Pure water 1,000

Seawater 1,025

Carbon disulfide 1,274

Chloroform 1,489

Tetrachloromethane (carbon tetrachloride) 1,595

Lead 11,340

Mercury 13,600