Question

Choose the reaction with negative $\Delta S$ value.

• A. $2 NaHCO _3( s ) \rightarrow Na _2 CO _3( s )+ CO _2( g )+ H _2 O ( g )$
• B. $Cl _2 (g) \rightarrow 2 Cl ( g )$
• C. $2 SO _2( g )+ O _2( g ) \rightarrow 2 SO _3( g )$
• D. $2 KClO _3( s ) \rightarrow 2 KCl ( s )+3 O _2( g )$

Answer 1

Answer: (C)

$\Delta S$ has negative value if number of gaseous moles decreases during a reaction, $\Delta n_g=-$ ve
For the reaction
$2 SO _2+ O _2 \longrightarrow 2 SO _3 $
$\Delta n_g=2-3=-1$