could anyone tell me why the molecular formula of agas is not always the same as the empirical formula

tnx

It may be a dimer or a trimer.
For example, CH is the empirical formula for acetylene but the molecular formula is HC(triple bond)CH or C2H2.

The molecular formula of a gas may not always be the same as the empirical formula because some gases can exist as dimers or trimers. This means that multiple molecules of the gas can bond together to form a larger molecule.

For example, let's consider acetylene. The empirical formula for acetylene is CH, which indicates that it consists of one carbon atom and one hydrogen atom. However, acetylene molecules can actually bond together to form larger molecules. The molecular formula of acetylene is HC(triple bond)CH or C2H2, which indicates the presence of two carbon atoms and two hydrogen atoms bonded together.

This phenomenon occurs when certain gases have the tendency to form stronger bonds between individual molecules. This can result in the formation of larger molecules, altering the molecular formula compared to the empirical formula. So, in the case of gases that can exist as dimers or trimers, their molecular formulas will differ from their empirical formulas.