To study the changes in the state of sublimate solids on heating.
Sublimation is a process in which a substance transitions directly from a solid to a gaseous phase without passing through the liquid phase. This physical change occurs when the substance is heated to a temperature that allows its particles to gain enough energy to break the intermolecular forces holding them in a solid state. Sublimation is the reverse process of deposition, where a gas transitions directly to a solid without becoming a liquid.
The enthalpy of sublimation is the energy that is computed. Only pressures and temperatures lower than a substance's triple point can cause sublimation. A substance's triple point is the pressure and temperature at which it will exist in its three phases—the solid, gaseous, and liquid phases. Below the triple point, solid water sublimates when its temperature rises and turns into gas.
Solid ⇌ Vapour (gas)
Examples of sublimation
Note: Sublimation occurs more efficiently when the air is dry, and the ice is near the melting point of water.
Application of Sublimation
The chemistry behind the reaction based on the experiment
Ammonium chloride changes directly from solid to gaseous state on heating. Hence, on heating ammonium chloride, it gets converted into white vapors. The gaseous form of ammonium chloride can be cooled quickly to get a pure solid.
Ammonium chloride is NH4Cl, decomposing into ammonia and hydrochloric acid when heated by thermal decomposition.
This dissociated molecule recombines on cooling to form NH4Cl.
Dissociation is a physical change that is also a chemical change because the change is reversible.
Learner will be able to