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Moles

Volumes of Gases - Avogadro's Law.

Avogadro's Law says that the same volume of gas
contains the same number of particles.
It does not matter what gas you have,
they all contain the same number of particles
 provided that they are at the same temperature and pressure.

This leads on to an even more useful fact.
At room temperature (25 °C) and one atmosphere pressure (101kPa),
one mole of any gas occupies a volume of 24,000 cm3 (24 litres).

The equation which converts moles into volume is

volume = moles x 24,000 cm3


Example 1.

What volume of carbon dioxide is produced by burning 6 g  of carbon in air?

Method.
1) Find how many moles of carbon are present in 6 g  of carbon.
RAM of C = 12.

moles = mass ÷ RAM

moles = 6 ÷ 12
                                 = 0·5 moles of carbon.


2) Write the equation for the reaction.

carbon + oxygen  arrow  carbon dioxide.
 C(s)  +    O2(g)   arrow          CO2(g)

Use the big numbers to find the proportion of reactant to product.
1C gives 1CO2, the proportion is 1 to 1,
so 0·5 moles of carbon will make 0·5 moles of carbon dioxide.

3) Convert moles into volume.

volume  =  moles x 24,000 cm3

volume  =  0·5 x 24,000 cm3
                                   = 12,000 cm3 of carbon dioxide.

So, burning 6 g  of carbon in air will produce 12,000 cm3 of carbon dioxide.

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