Definition and examples of specific volume

The SI unit for specific volume is cubic metres per kilogram (m ³ / kg). However, it may be expressed in other units of volume by mass, including millilitres per gram (mL/g) or cubic feet per pound (ft/lb). ³ / lb).

Specific volume formulas

There are three common specific volume formulas:

1. ν = V / m where V is the volume andm is the mass
2. ν = 1 / ρ = ρ ^-1 where ρ is the density
3. ν = RT / PM where R is the ideal gas constant, T is the temperature, P is the pressure and M is the molar mass

The first equation applies to all states of matter.

The second equation is mainly concerned with gases and liquids, as they are relatively incompressible so their density does not depend much on temperature or pressure.

The third equation applies to ideal gases or the approximate behaviour of real gases at low temperatures and pressures.

The specific volume is intrinsic and intensive

Because the specific volume is per unit mass, its value does not depend on the size of the sample. It is therefore an intrinsic and intensive property of matter. The specific volume values are the same regardless of where a substance is sampled.

Example calculations

You have 5 kg of air in a 0.037 m tank. ³What is the specific volume of air?

ν = V / m
ν = 0.037 m ³ / of 5 kg = 0.0074 m ³ / kg

The density of the silver is 10.49 g / cm ³What is its specific volume?

ν = 1 / ρ
ν = 1 /(10,49 g / cm _³ ) = 0.095 cm ³ / g

Table of specific volume values

The tables list specific volume values, usually along with density values. Most of the time, the values are at standard temperature and pressure (STP), which is 0 °C (273.15 K, 32 °F) and 1 atm.

Substance	Density	Specific volume
	(kg / m 3 )	(m 3 / kg)
Air	1.225	0,78
Ice	916,7	0,00109
Water (liquid)	1000	0,00100
Salt water	1030	0,00097
Mercury	13546	0,00007
R-22 *	3,66	0,273
Ammonia	0,769	1,30
Dioxide carbon	1.977	0,506
Chlorine	2.994	0.334
Hydrogen	0.0899	11.12
Methane	0,717	1,39
Nitrogen	1,25	0,799
Steam*	0,804	1,24

Substances marked with an asterisk (*) are not in PTS.

More extensive tables are available for a variety of temperature and pressure values for refrigerants, air and vapour.

Specific Volume Uses

Specific volume finds use in engineering, chemistry and physics. Although the concept applies to any state of matter, it is generally used to make predictions about the behaviour of gases under changing conditions. It is applied to volume, molar volume and partial molar volume calculations.

For example, consider a sealed chamber containing a fixed number of gas molecules:

• If the density of the gas is doubled, its specific volume is halved.
• If the specific volume is doubled, the density is halved.
• If the chamber expands (increases in volume) while the number of molecules remains constant, the density of the gas decreases and the specific volume increases.
• If the chamber contracts (decreases in volume) while the number of molecules remains constant, the density of the gas increases and the specific volume decreases.
• If some molecules are removed but the volume remains constant, the density decreases and the specific volume increases.
• If some molecules are added but the volume remains constant, the density increases and the specific volume decreases.

Specific volume vs. specific gravity

Specific gravity is the ratio of the density of one substance to the density of another substance. Since specific volume is the reciprocal of density, it can be used to determine specific gravity.

For example, specific gravity predicts whether a substance will float or sink in another substance. If substance A has a specific volume of 0.358 cm ³ / gand substance B has a specific volume of 0.374 cm ³ / g, taking the reciprocal of each value gives the density. Then, the density of A is 2.79 g / cm ³ and the density of B is 2.67 g / cm ³. The specific gravity, comparing the density of A to B is 1.04 or the specific gravity of B compared to A is 0.95. A is denser than B, so A sinks in B or B floats in A.