Question

For which of the following reactions, $\Delta$H is equal to $\Delta$U?

• A. $2HI\left(g\right)\to H_2\left(g\right)+I_2\left(g\right)$
• B. $2S{O}_2\left(g\right)+O_2\left(g\right)\to 2S{O}_3\left(g\right)$
• C. $N_2\left(g\right)+3H_2\left(g\right)\to 2N{H}_3\left(g\right)$
• D. $2N{O}_2\left(g\right)\to N_2{O}_4\left(g\right)$

Answer 1

The correct option is A $2HI\left(g\right)\to H_2\left(g\right)+I_2\left(g\right)$

For the reaction, $2HI\left(g\right)\to H_2\left(g\right)+I_2\left(g\right)$, $\Delta$H is equal to $\Delta$U

$\Delta$H $=\Delta$U $+\Delta$nRT

For the reaction, $2HI\left(g\right)\to H_2\left(g\right)+I_2\left(g\right)$, $\Delta$n $=1+1-2=0$

Hence, $\Delta$H $=\Delta$U $+\left(0\right)$RT

$\Delta$H $=\Delta$U

Note: $\Delta$n is the difference between the number of moles of gaseous products and the number of moles of gaseous reactants.