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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
cm^{3}.

24,000
cm^{3} is the same volume as 24
litres.

The equation which converts moles into volume is

volume = moles x
24,000 cm^{3}

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
carbon
dioxide.

C_{(s)} +
O_{2(g)} CO_{2(g)}

Use the big numbers to find the proportion of reactant to product.

1C gives 1CO_{2}, 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
cm^{3}

volume = 0·5 x
24,000 cm^{3}

= 12,000 cm^{3} of
carbon dioxide.

So, burning 6 g of
carbon in air

will produce 12,000
cm^{3} of carbon
dioxide.

Links Moles Revision Quizzes Revision Questions

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