Match the transformations in column I with appropriation options in column II. (A) CO2 (s)→CO2 (g)

Question

Match the transformations in column I with appropriation options in column II. 

Column I	Column II
(A) CO2 (s)→CO2 (g)	(p) Phase transition
(B) CaCO2 (s) →CaO(s) + CO2 (g)	(q) Allotropic change
(C) 2H → H2 (g)	(r) ∆H is positive
(D) P(white, solid) → P(red, solid)	(s) ∆S is positive
	(t) ∆S is negative

Answer 1

Correct option A → p, r, s; B → r, s; C → t; D → p, q, t

Explanation:

 (A) CO₂ (s)→ CO₂ (g)

It is just a phase transition (sublimation) as no chemical change has occurred. Sublimation is always endothermic. Product is gas, more disordered, hence ∆S is positive.

(B) CaCO₃ (s)→ CaO(s) + CO₂ (g)

It is a chemical decomposition, not a phase change. Thermal decomposition occur at the expense of energy, hence endothermic. Product contain a gaseous species, hence, ∆S > 0.

(C) 2H→ H₂ (g)

A new H–H covalent bond is being formed, hence ∆H < 0.

Also, product is less disordered than reactant, ∆S < 0.

(D) Allotropes are considered as different phase, hence P_{(white, solid)}→ P_{(red, solid)} is a phase transition as well as allotropic change.

Also, red phosphorus is more ordered than white phosphorus, ∆S < 0.