How a solid is formed by reaction between gas and gas?

Answer 1

Whether a substance is a solid, a liquid, or a gas depends on the nature of the bonds within the substance, the strength of attraction between molecules, and the size of the molecules. When a chemical reaction occurs, these bonds are reconfigured, sometimes leading to a change of state.

For example, hydrogen chloride (HCl) and ammonia (NH3) are both gasses at room temperature. The attraction between molecules is farily strong, but not enough to keep such small molecules in a liquid or solid stateat room temperature. When they meet, they react, forming ammonion chloride:

NH3 + HCl --> NH4Cl.

This is an ionic compound, with a strong attraction between ammonium ions (NH4+) and chloride ions (Cl-). So, instead of forming discreet molecules, they arrange into a solid crystal lattice.

Another reaction is that between silane (SiH4) and oxygen (O2), both are gasses with very weak attraction between molecules.

The reaction then proceeds like this:

SiH4 + 2O2 --> SiO2 + 2H2O

Instead of forming simple molecules, the silica (SiO2) forms a covalent network where very silicon atom is bonded to four oxygen atoms, and every oxygen atom is bonded to two silicon atoms.