Question

For the reaction, $FeC{O}_{3\left(s\right)}\to$ $Fe{O}_{\left(s\right)}$ + $C{O}_{2\left(g\right)}$; $\Delta H=82.8kJ$ at $25C$, what is ($\Delta E$ or $\Delta U$) at ${25}^{o}C$?

• A. $82.8kJ$
• B. $80.32kJ$
• C. $-2394.77kJ$
• D. $85.28kJ$

Answer 1

The correct option is B $80.32kJ$

Solution:- (B) $80.32kJ$

For the given reaction-

${FeC{O}_3}_{\left(s\right)}⟶{FeO}_{\left(s\right)}+{C{O}_2}_{\left(g\right)}$

$\Delta n_g=n_P-n_R=1-0=1$

$\Delta H=82.8kJ$

$T=25℃=(25+273)K=298K$

Now as we know that,

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

$\Rightarrow \Delta U=\Delta H-\Delta n_{g}RT$

$\Rightarrow \Delta U=82.8-(1\times 8.314\times {10}^{-3}\times 298)$

$\Rightarrow \Delta U=82.8-2.48=80.32kJ$

Hence the value of $\Delta U$ or $\Delta E$ at $25℃$ is $80.32kJ$.