One of the fundamental topics in chemistry is calculating between volume and moles of a gas.

In chemistry, you hear people mention “at STP”.  STP means standard temperature and pressure.  Standard pressure is 1 atmosphere; standard temperature, curiously, is 0°C.

The relevance of standard temperature and pressure is that, at those particular settings, the volume of an ideal gas is 22.4L/mole.  Note that the molar volume is independent of the molar mass of the gas, so long as it closely follows the “ideal gas” concept.  Mortimer reports that, at STP, most gases closely follow ideal behaviour.

Example:  Find the volume of 1.000 kg of CO₂ at STP.

Solution: We must first convert the mass to moles (see my post here and perhaps even here for more about that), as follows (M.M. meaning molar mass):

From the periodic table of the elements, M.M. of CO₂=12.0g+2(16.0g)=44.0g

We proceed with our conversion from kilograms to L, using the factor 22.4L/mol:

1) 1.000kg=1000.g

2) 1000.g x 1mol CO₂/44.0g = 22.7273mol CO₂

3) 22.7273mol CO₂ x 22.4L/mol = 509L CO₂

The one-line chemistry method you might see on the board combines the steps:

1.000kg x 1000.g/kg x 1mol CO₂/44.0g x 22.4L/mol = 509L CO₂

Apparently, based on the molar volume of 22.4L/mol, 1.000kg of CO₂ has volume 509L at STP (1 atmosphere and 0°C).

There is much more to say about volumes of gases. I’ll be talking more about them in future posts.

HTH:)

Source:

Mortimer, Charles E. Chemistry, 6th Ed. Belmont: Wadsworth, 1986.

Jack of Oracle Tutoring by Jack and Diane, Campbell River, BC.