Question

Which of the following processes does not occur at the interface of phases?
(A) Crystallization
(B) Heterogeneous catalysis
(C) Homogeneous catalysis
(D) Corrosion

Answer 1

Hint: (1) By the term phase, we mean a distinct and homogeneous state of a system which is not separated into parts by any visible boundaries. Solid, liquid and gas are the three fundamental phases of matter but many other phases like amorphous, crystalline, colloid are also known to exist.
 (2) When a phase is converted from one form to another form, a phase change or a phase conversion is said to have taken place. For example, water can convert from its liquid phase to its solid phase and also to its steam or gaseous phase.
(3) By the term interface, we mean a surface which acts as a common boundary between two phases.

Complete step by step answer:
Crystallization refers to the process by which a solid is formed in which the atoms or molecules are highly arranged or organized in a structure called crystal. Crystals are generally formed by evaporative or cooling crystallization or precipitation. So basically, it involves the formation of a new phase from an old phase. So the formation of crystals will take place at the interface of phases and so, option A is incorrect.
Heterogeneous catalysis is a catalytic reaction in which the catalyst phase differs from the reactant or the product phase. It typically involves gaseous reactants and solid catalysts. So, this process also occurs at the interface of phases and hence B is incorrect.
Homogeneous catalysis is a reaction in which the catalyst phase, the reactant phase and the product phase are all the same. So this does not occur at the interface of phases. So, option C is correct.
Corrosion is a natural process by which refined metals are converted into chemically stable forms like oxides, sulphides etc. Thus, chemical reactions occur at the interface between the metal and its environment. So, D is incorrect.

Note: The production of acetic acid is an example of homogeneous catalysis. Enzymes like carbonic anhydrase are also homogeneous catalysts. It can catalyse the release of carbon dioxide from the blood into the lungs. Although homogeneous catalysts are more selective than heterogeneous catalysts, the separation of homogeneous catalysts from the products is very difficult.