This can be verified using the ideal gas equation. Consider two gases 1 and 2. The gas equation for each gas is:

Gas 1: P

Now if P

The volume of one mole of any gas at STP is 22.4 litres. A mole of any substance contains 6.02x10^{23} molecules – a number known as Avogadro’s number or Avogadro’s constant.

Avogadro's constant is the number of particles in a mole of the substance. This number is always the same.

So in:

1 mole of hydrogen (2 g) there are 6.02x10

1 mole of oxygen (32 g) there are 6.02x10

1 mole of copper (63 g) there are 6.02x10

1 mole of uranium 235 (235 g) there are 6.02x10

For example if we have 2 kg of uranium in a fuel rod we have 2000/235 = 8.51 moles and this contains 8.51x6.02x10

Dalton's law of partial pressures

If two or more gases are mixed in a container then the final pressure can be found from Dalton's law, which states that:

The pressure in a container is the sum of the partial pressures of the gases that occupy the container.

The partial pressure of a gas is that pressure that the gas would exert if it alone occupied the container.

For example, consider a container with a volume V and a temperature T. Let the container be occupied by two different gases, there being n

Now P

But the total pressure in the container is P, where PV = nRT for n = n

Therefore:

or

A useful application of this law is in cases where volumes of the same gas occupy separate but connected containers at differing temperatures.

Example problem A volume of gas V at a temperature T

If the stopcock is opened the temperature of the gas in the second sphere becomes T

Show that the final pressure p’ within the apparatus is: p’ = 2pT

Let there be a molecules of gas, and let there be n

Now n= n

Therefore: p/T