To Study the Changes in the State of Sublimate Solids on Heating

Objective

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

 

Theory 

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 realistic and detailed representation of digital images made possible by dye-sublimation printers is helpful when researching substances.  
  • Chemists frequently use sublimation to purify volatile compounds. 
  • It is possible to reveal latent fingerprints on paper using iodine sublimation.  
  • Sublimation purifies compounds. It is especially advantageous for organic compounds.  
  • Dry ice produces the illusion of fog because it sublimates so quickly.  

 

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. 

NH4Cl[s]→NH3[g]+HCl[l] 

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. 

 

Learning Outcomes

Learner will be able to 

  • Describe the process of sublimation. 
  • Describe the examples and applications in the sublimation process. 
  • Understand the chemistry behind the reaction.