Question

According to Avogadro's Law, "Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules". But how is this statement correct? How do we know that equal number of molecules are present in two gases taken in equal volumes?

Even if we consider equal volumes of any two gases(let's consider two gases for example) contain equal number of molecules, if we have the two gases in two containers of same volumes, we can add more gas to any one container and increase the density of the gas inside the container. In that case, the volume of the gas remains equal to the volume of the container but the number of gas molecules inside the container has increased and there is no chage to the number of molecules of the other gas we took inside a similar container. So now we have equal volumes of two gases but we have increased the number of molecules of one gas so now how can we say that the equal volumes of these two gases contain equal number of molecules?

If we take equal number of molecules of two gases and contain one of the gas in a container of some volume and the other gas in a container of a different volume, we will have unequal volumes of two gases having equal number of particles.

So how is Avogadro's Law explained?

Answer 1

Avogadro's Law, "Equal volumes of gases at the same temperature and pressure contain equal numbers of molecules".

In this example, we keep the volume constant, but we increased the number of molecules. Please note that as per Avogadro's law, the temperature and pressure also need to be the same. As we increase the number of molecules in one container, the temperature and pressure changes, which violates Avogadro's law. So, unless we keep all the parameters, ie pressure, temperature and volume Avogadro's law will be violated.