Question

Match the transformations in Column I with appropriate options in Column II:

Column I		Column II
A	$CO _{2}(s) \rightarrow CO _{2}(g)$	P	Phase transition.
B	$CaCO _{3}(s) \rightarrow$ $CaO (s)+ CO _{2}(g)$	Q	Allotropic change.
C	$2 H \rightarrow H _{2}(g)$	R	$\Delta H$ is positive.
D	$P_{\text {(white, solid) }} \rightarrow P_{\text {(red, solid) }}$	S	$\Delta S$ is positive.
		T	$\Delta S$ is negative.

• A. $( A ) \rightarrow( P ),( Q ),( S ) ;( B ) \rightarrow( R ),( S ) ;( C ) \rightarrow( T ) ;( D ) \rightarrow( P )$ $( R ),( T )$
• B. $( A ) \rightarrow( P ),( R ),( S ) ;( B ) \rightarrow( R ),( S ) ;( C ) \rightarrow( T ) ;( D ) \rightarrow( Q )$, $( R ),( T )$
• C. $( A ) \rightarrow( P ),( R ),( S ) ;( B ) \rightarrow( P ),( S ) ;( C ) \rightarrow( T ) ;( D ) \rightarrow( Q )$ (S), (T)
• D. $( A ) \rightarrow( P ),( Q ),( S ) ;( B ) \rightarrow( R ),( S ) ;( C ) \rightarrow( R ) ;( D ) \rightarrow( Q )$ $( R ),( T )$

Answer 1

Answer: (B)

For the given changes:
(A) $CO _{2}(s) \xrightarrow{\Delta} CO _{2}$ (g) Phase transition,
$\Delta H =+$ ve and $\Delta S =+$ ve
(B) $CaCO _{3} (s) \xrightarrow{\Delta} CaO (s)+ CO _{2}(g)$
No phase transition, $\Delta H =+$ ve and $\Delta S =+ ve$
(C) $2 H \rightarrow H _{2}(g)$
Two particles give one gaseous particle,
so $\Delta S=-v e$
(D) $P_{\text {(white, solid) }} \xrightarrow{\Delta} P_{\text {(red, solid) }}$
This is an allotropic change. $\Delta H$ is positive, as white phosphorus converts to red phosphorus on heating.
$\Delta S$ is negative, as red phosphorus is a polymeric solid, less reactive than white phosphorous.