Our Objective

To study the changes in the state of sublimate solids on heating.

The Theory 

Sublimation is the process by which substances transition from one state to another, such as from solid to gas. Sublimation transfers material from the solid to the gaseous phase without transitioning to the liquid phase. This endothermic phase transition happens at temperatures and pressures lower than the substance's triple point. The triple point is the point at which a substance's pressure and temperature are such that it may exist simultaneously in all three states of matter. A substance's triple point is a distinguishing feature.  DE sublimation, also known as deposition, is the process by which a gas is turned directly into a solid state. 

Solid ⇌ Vapour (gas) 

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 vapours. The gaseous form of ammonium chloride can be cooled easily to get a pure solid. 

Ammonium chloride is NH₄Cl, which decomposes into ammonia and hydrochloric acid when heated by the process of thermal decomposition. 

NH_4​Cl[s]→NH₃​[g]+HCl[l] 

This dissociated molecule recombines on cooling to form NH₄Cl 

Dissociation is a physical change that also happens to be a chemical change because the change is reversible. 

Examples of sublimation 

• Dry ice, a frozen form of carbon dioxide, is the most excellent illustration of sublimation. When dry ice is exposed to air, it changes its phase from solid to gaseous, resulting in fog. The gaseous state of frozen carbon dioxide is more stable than the solid state.  
• Naphthalene, an organic chemical, is another well-known example of sublimation. Naphthalene is commonly found in insecticides like mothballs. Because of the existence of non-polar molecules bound together by Van Der Waals intermolecular interactions, this organic complex sublimes. Naphthalene sublimes to create vapours when heated to 176°F. It destabilises on chilly surfaces, forming needle-like crystals.

Note: Sublimation occurs more efficiently when the air is dry, and the ice is near the melting point of water. 

Application of Sublimation 

• Dye-sublimation printers aid in the detailed and realistic portrayal of digital images, which aids in investigating chemicals.  
• Chemists often use sublimation to purify volatile substances. 
• Iodine sublimation can be used to expose latent fingerprints on paper. 
• Compounds are purified by sublimation. It is particularly beneficial for organic molecules. 
• Because dry ice sublimates so quickly, it is utilised to create fog effects. 

Learning Outcomes

1. The learner will be able to describe the sublimation process. 
2. The learner will be able to describe the process of deposition (also known as sublimation). 
3. Note: Deposition is the opposite procedure in which evaporated air condenses and re-forms the solid. 
4. The learner acquires basic laboratory skills.