Question

For the gas phase reaction,
$P{Cl}_5\left(g\right)\rightleftharpoons P{Cl}_3\left(g\right)+{Cl}_2\left(g\right)$
Which of the following conditions are correct?

• A. $\Delta H<0$ and $\Delta S<0$
• B. $\Delta H>0$ and $\Delta S<0$
• C. $\Delta H=0$ and $\Delta S<0$
• D. $\Delta H>0$ and $\Delta S>0$

Answer 1

The correct option is D $\Delta H>0$ and $\Delta S>0$

${PCl}_5\left(g\right)\rightleftharpoons {PCl}_3\left(g\right)+{Cl}_2\left(g\right)$

$\Delta H=\Delta U+\Delta n_{g}RT$

${\Delta n}_g=2-1=1$

$\Delta H=\Delta U+RT$

$\Delta U>0$ and $R,T>0$

$\therefore \Delta H>0$

The number of molecules are increased in the product. Therefore randomness increases.

Therefore, $\Delta S>0$