Explanation: Aqueous solution, melt, glass or gel, is usually homogenous, single phase and amorphous. This may greatly facilitate formation of crystalline product, since long range diffusion of ions may not be necessary and the product my form at lower temperature.

Explanation: Crystalline phases are prepared at low temperature range such as 25-100 degree Celsius whereas much high temperatures would be required for a normal solid state synthesis. Crystals usually form at low temperatures but due to the release of heat of fusion during crystallization, the entropy of the universe increases thus the second law of thermodynamics is not altered.

Explanation: Zeolites are hydrated Aluminosilicate framework structures which contain large channels and cavities such that a variety of organic and inorganic substances may enter the zeolite structure.

Explanation: Starting materials for zeolite structures are aqueous solution of silicate and aluminate anions which are mixed together with alkali. A gel forms by a process of copolymerization of the silicate and aluminate anions and on subsequent heat treatment, under a high water vapour pressure, crystals of zeolite are produced.

Explanation: Melts are high temperature liquids whereas solutions are liquids at low temperatures. Thus on melting together the solid starting materials, complete homogenization occurs and recrystallization takes place on subsequent cooling of the melt.

Explanation: Crystallization of melts is a valuable method for growing single crystals since in the presence of liquid phase and in the absence of too many crystal nuclei, large crystals readily grow.

Explanation: Li2Si2O5 is a glass ceramic material, which is a crystalline material of glassy intermediates and an important component of several commercial glass-ceramics. Crystalline Li2Si2O5 melts at 1032oC.

Explanation: Transition temperature is the temperature region where the polymer transition occurs from a hard, glassy material to a soft, rubbery material. Transition temperature required during the preparation of lithium disilicate is 450oC and on heating at 500 to 700oC crystallization of LI2Si2O5 occurs readily after few hours.

Explanation: The formation of gaseous PtO2 at 1200oC or higher is an endothermic reaction which can be used for chemical transport. The PtO2 diffuses at lower temperatures where it may deposit well-formed crystals of platinum metal.

Explanation: Van Arkel method is used for the purification of certain metals makes uses of an exothermic reaction between metal and iodine to form a gaseous iodide, example CrI2. Since the formation of metal iodide is exothermic, and so the metal is redeposited at a higher temperature.

Explanation: Van Arkel method is a purification method which uses metal and iodine to form gaseous iodide, it transports two substances in opposite directions along the temperature gradient and this is possible when one reaction is exothermic and the other is endothermic.

The gaseous SnO subsequently reacts with CaO and CO2.

Explanation: Aluminium and sulphur react very slowly during the preparation of aluminium sulphide since liquid Al becomes coated with a skin of Al2S3, which acts as a diffusion barrier to further reaction.

Explanation: Metallic niobium and silica when heated at vacuum at 1100oC, they do not react together at all hence no product will be formed. But in the presence of traces of H2 gaseous SiO forms and migrates to the niobium.

Explanation: Gases react much more quickly than do solids because mobilities are increased. In addition, the gaseous phase is often important in normal solid state reactions under isothermal conditions where it may act as a rapid means of transporting matter from one crystal to another.