View source for Molar volume of a gas

The volume of a gas is sensitive to both pressure and temperature. Because a gas is easily compressible, by adjusting the pressure and temperature of a gas sample, the volume that the gas sample occupies can be altered. Therefore, if the volumes of any two gas samples are to be compared, they must be under the same conditions (ie - the two gas samples MUST be at the same temperature and pressure).

A common set of conditions that is often used by scientists is called '''Standard Temperature and Pressure''' or '''STP'''. When the STP condition is implied, scientists know that the gas must be at a specific temperature and a specific pressure. The conditions used for reference are:
* standard temperature is 273 K (or 0<sup>o</sup>C).
* standard pressure is 1 atm (760 torr) 

== Gas densities at STP==
For any gas at STP, when the molar mass of the gas is divided by the density of the gas, the value "22.4" is always obtained.
Take a look at the "special" number, "22.4". 	

[[File:molarvolume.gif]]

Or,

  <b>density of a gas = <sup>molar mass</sup> / <sub>molar volume</sub></b>

{| width="600"

| <b>Gas</b>
| <b>Molar Mass<br/>(g/mole)  </b>
| <b>Density at STP <br/>(g/L)  </b>	
| <b>Molar Mass/Density <br/>(L/mole)</b>
|-
| N<sub>2</sub>, nitrogen gas 	
| 28.014
| 1.25
| <font color="red">22.4</font>
|-
| O<sub>2</sub>, oxygen gas 	
| 31.998
| 1.43
| <font color="red">22.4</font>
|-
| CH<sub>4</sub>, methane gas 	
| 16.043
| 0.714
| <font color="red">22.4</font>
|-
| CO<sub>2</sub>, carbon dioxide 	
| 44.009
| 1.96
| <font color="red">22.4</font>
|-
| H<sub>2</sub>, hydrogen gas 	
| 2.015
| 0.090
| <font color="red">22.4</font>
|-
| Ar, argon gas 	
| 39.948
| 1.78
| <font color="red">22.4</font>
|}

The molar volume of any gas at STP is  <b>22.4 L</b>.

 The unit of 22.4 is <font color="red"><sup>L</sup>/<sub>mole</sub></font>.

== Molar volume calculations==
Using conversion factors, we can solve questions involving conversion:

{|cellpadding="5" align="center"  border="1" width="500"
|-
|align="right"|from '''moles of gas''' to '''volume occupied at STP'''  [[File:reactionarrow.gif]]
|align="center"|×  22.4 L/mole  
|-
|align="right"|from '''volume occupied at STP''' to '''moles of gas'''  [[File:reactionarrow.gif]]
|align="center"|÷ 22.4 L/mole 
|}

==External link==
<span class="pops">[http://www.wisc-online.com/Objects/ViewObject.aspx?ID=GCH5704 How to calculate gas density from the molar volume under STP conditions.]</span>

==Content suitability==
BCIT courses:
<span class="pops">[http://www.bcit.ca/study/outlines/chem0011  CHEM 0011]</span>