Question

For the gas-phase decomposition ,
$PC{I}_5\left(g\right)\begin{array}{c}△\rightleftharpoons \end{array}PC{I}_3\left(g\right)+C{I}_2\left(g\right)$:

• A. $△H<0,△S<0$
• B. $△H>0,△S>0$
• C. $△H>0,△S<0$
• D. $△H<0,△S>0$

Answer 1

The correct option is B $△H>0,△S>0$

Given reaction is the decomposition reaction of $PC{l}_5$.

Usually, all the decomposition reactions are endothermic, heat energy is absorbed during the reaction. Hence enthalpy of the reaction is positive.

$\Delta H>0$ or positive

In the reaction, 1 mol of $PC{l}_5$ gives the 2 mol of gaseous product. This means that there is an increase in randomness or the entropy of the reaction. Hence we can say that $\Delta S>0$ or positive.