Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications!

The Ideal Gas Law

The relationship between volume, pressure, temperature and quantity of a gas, including definition of gas density.

Sponsored Links

In a perfect or ideal gas the correlations between pressure, volume, temperature and quantity of gas can be expressed by the Ideal Gas Law.

The Universal Gas Constant, R u is independent of the particular gas and is the same for all "perfect" gases, and is included in of The Ideal Gas Law:

p V = n R u T (1)

where

p = absolute pressure [N/m2], [lb/ft2]

V = volume [m3 ], [ft3 ]

n = is the number of moles of the gas present

R u = universal gas constant [J/mol K], [lb f ft/(lb mol o R)]= 8.3145 [J/mol K]= 0.08206 [L atm/mol K]  = 62.37 [L torr /mol K]

T = absolute temperature [K], [ o R]

For a given quantity of gas, both n and R u are constant, and Equation (1) can be modified to

p 1 V 1 / T 1 = p2V2/ T2(2)

expressing the relationship between different states for the given quantity of the gas.

Equation (1)  can also be expressed as

p V = N k T                         (3)

N =number of molecules

k = Boltzmann constant = 1.38066 10 -23 [J/K] = 8.617385 10 -5 [eV/K]

  • One mole of an ideal gas at STP occupies 22.4 liters.

The Ideal Gas Law and the Individual Gas Constant - R

The Ideal Gas Law - or Perfect Gas Law - relates pressure, temperature, and volume of an ideal or perfect gas . The Ideal Gas Law can be expressed with the Individual Gas Constant .

p V = m R T                     (4)

where

p = absolute pressure [N/m2], [lb/ft2]

V = volume [m3 ], [ft3 ]

m = mass [kg], [ slugs ]

R = individual gas constant [J/kg K], [ft lb/slugs o R]

T = absolute temperature [K], [ o R]

This equation (3) can be modified to:

p = ρ R T                         (5)

where the density

ρ = m / V  [kg/m3 ], [slugs/ft3 ]                    (6)

The Individual Gas Constant - R - depends on the particular gas and is related to the molecular weight of the gas.
See also Non-ideal gas - Van der Waal's equation and constants , used to correct for non-ideal behavior of gases caused by intermolecular forces and the volume occupied by the gas particles and how to calculate total pressure and partial pressures from Ideal gas law

Example: The Ideal Gas Law

A tank with volume of 1 ft3 is filled with air compressed to a gauge pressure of 50 psi. The temperature in tank is 70 o F .

The air density can be calculated with a transformation of the ideal gas law (5) to:

ρ = p / (R T)                            (7)

ρ = ((50 [lb/in2]+ 14.7 [lb/in2])*144 [in2/ft2]) / (1716 [ft.lb/slug. o R]* (70+ 460)[°R])

= 0.0102 [slugs/ft3 ]

The weight of the air is the product of specific weight and the air volume. It can be calculated as:

w = ρ g V                               (8)

w = 0.0102 [slugs/ft3 ] * 32.2 [ft/s2]*1 [ft3 ]

= 0.32844 [slugs ft/s2]

= 0.32844 [lb]

Note!

The Ideal Gas Law is accurate only at relatively low pressures and high temperatures. To account for deviation from the ideal situation an other factor is included. It is called the Gas Compressibility Factor, or Z-factor. This correction factor is dependent on pressure and temperature for each gas considered.

The True Gas Law, or the Non-Ideal Gas Law, becomes:

P V = Z n R T                           (7)

where

Z = Gas Compressibility Factor

n = number of moles of gas present

Compressibility factor - Z - for Air

For full table - rotate the screen!

Compressibility factor for Air - Z -
Temperature
[K]
Pressure [ bar absolute]
1 5 10 20 40 60 80 100 150 200 250 300 400 500
75 0.005 0.026 0.052 0.104 0.206 0.308 0.409 0.510 0.758 1.013
80 0.025 0.050 0.100 0.198 0.296 0.393 0.489 0.726 0.959 1.193 1.414
90 0.976 0.024 0.045 0.094 0.187 0.278 0.369 0.468 0.678 0.893 1.110 1.311 1.716 2.111
100 0.980 0.887 0.045 0.090 0.178 0.264 0.350 0.434 0.639 0.838 1.040 1.223 1.594 1.954
120 0.988 0.937 0.886 0.673 0.178 0.256 0.337 0.413 0.596 0.772 0.953 1.108 1.509 1.737
140 0.993 0.961 0.921 0.830 0.586 0.331 0.374 0.434 0.591 0.770 0.911 1.039 1.320 1.590
160 0.995 0.975 0.949 0.895 0.780 0.660 0.570 0.549 0.634 0.756 0.884 1.011 1.259 1.497
180 0.997 0.983 0.966 0.931 0.863 0.798 0.743 0.708 0.718 0.799 0.900 1.007 1.223 1.436
200 0.998 0.989 0.977 0.954 0.910 0.870 0.837 0.814 0.806 0.855 0.931 1.019 1.205 1.394
250 0.999 0.996 0.991 0.982 0.967 0.955 0.946 0.941 0.945 0.971 1.015 1.070 1.199 1.339
300 1.000 0.999 0.997 0.995 0.992 0.990 0.990 0.993 1.007 1.033 1.067 1.109 1.207 1.316
350 1.000 1.000 1.000 1.001 1.004 1.008 1.012 1.018 1.038 1.064 1.095 1.130 1.212 1.302
400 1.000 1.001 1.003 1.005 1.010 1.016 1.023 1.031 1.053 1.080 1.109 1.141 1.212 1.289
450 1.000 1.002 1.003 1.006 1.013 1.021 1.029 1.037 1.061 1.091 1.118 1.146 1.209 1.278
500 1.000 1.002 1.003 1.007 1.015 1.023 1.032 1.041 1.065 1.091 1.118 1.146 1.205 1.267
600 1.000 1.002 1.004 1.008 1.016 1.025 1.034 1.043 1.068 1.092 1.117 1.143 1.195 1.248
800 1.000 1.002 1.004 1.008 1.016 1.024 1.032 1.041 1.062 1.084 1.106 1.128 1.172 1.215
1000 1.000 1.002 1.004 1.007 1.014 1.022 1.029 1.037 1.056 1.074 1.095 1.113 1.152 1.189
Sponsored Links

Related Topics

  • Air Psychrometrics

    Moist and humid air calculations. Psychrometric charts and Mollier diagrams. Air-condition systems temperatures, absolute and relative humidities and moisture content in air.
  • Basics

    Basic engineering data. SI-system, unit converters, physical constants, drawing scales and more.
  • Fluid Mechanics

    The study of fluids - liquids and gases. Involving velocity, pressure, density and temperature as functions of space and time.
  • Gases and Compressed Air

    Properties of air, LNG, LPG and other common gases. Pipeline capacities and sizing of relief valves.

Related Documents

Sponsored Links

Search

Search is the most efficient way to navigate the Engineering ToolBox.

Engineering ToolBox - SketchUp Extension - Online 3D modeling!

3D Engineering ToolBox Extension to SketchUp - add parametric components to your SketchUp model

Add standard and customized parametric components - like flange beams, lumbers, piping, stairs and more - to your Sketchup model with the Engineering ToolBox - SketchUp Extension - enabled for use with older versions of the amazing SketchUp Make and the newer "up to date" SketchUp Pro . Add the Engineering ToolBox extension to your SketchUp Make/Pro from the Extension Warehouse !

Translate this Page

Translate this page to Your Own Language .

About the Engineering ToolBox!

Privacy Policy

We don't collect information from our users. More about

Citation

This page can be cited as

  • The Engineering ToolBox (2003). The Ideal Gas Law. [online] Available at: https://www.engineeringtoolbox.com/ideal-gas-law-d_157.html [Accessed Day Month Year].

Modify the access date according your visit.

3D Engineering ToolBox - draw and model technical applications! 2D Engineering ToolBox - create and share online diagram drawing templates! Engineering ToolBox Apps - mobile online and offline engineering applications!

Unit Converter

















































3.15.9

Sponsored Links
.