Question

For a gaseous reaction, $A\left(g\right)+3B\left(g\right)\to 3C\left(g\right)+3D\left(g\right)$
$△E$ is $17Kcal$ at ${27}^{\circ }C$ assuming $R=2cal{K}^{-1}mo{l}^{-1}$ the value of $△H$ for the above reaction is

• A. $15.8kcal$
• B. $18.2kcal$
• C. $20.0kcal$
• D. $16.4kcal$

Answer 1

Answer: (A)

$15.8kcal$

As for a reaction $\Delta E$ = $\Delta H$ +$\Delta n_{g}RT$

$\Delta n_g$ = number of gaseous products - number of gaseous reactants

T = 300K and $\Delta E$ = 17KCal and $\Delta n_g$ = 3 +3 -3-1 =2

$\Delta H$ = $\Delta E$ - $\Delta n_{g}RT$

$\Delta H$ = 17000 Cal - 2 X 2 X 300 Cal = 15800 Cal

$\Delta H$ = 15.8KCal