Question

For which one of the following reactions will there be a positive $\Delta S$ ?

• A. $H _{2} O (g) \longrightarrow H _{2} O (l)$
• B. $H _{2}+ I _{2} \longrightarrow 2 HI$
• C. $CaCO _{3}(s) \longrightarrow CaO (s)+ CO _{2}(g)$
• D. $N _{2}(g)+3 H _{2}(g) \longrightarrow 2 NH _{3}(g)$

Answer 1

Answer: (C)

$CaCO _{3}(s) \longrightarrow CaO (s)+ CO _{2}(g)$

Answer 2

$\Delta S$ (entropy change) is the measure of randomness and thus in solid, liquid and gas, the order of entropy is gas $>$ liquid $>$ solid Thus, $\Delta S$ is positive for the reaction