Question

Assume each reaction is carried out in an open container. For which reaction will ∆H = ∆E?

• A. H2(g) + Br2(g) $→$ 2HBr(g)
• B. C(s) + 2H2O(g) $→$ 2H2(g) + CO2(g)
• C. PCl5(g) $→$ PCl3(g) + Cl2(g)
• D. 2CO(g) + O2(g) $→$ 2CO2(g)

Answer 1

Answer: (A)

H2(g) + Br2(g) $→$ 2HBr(g)

Answer 2

As We know that, $△H=△U+△PV$
But for a physical or chemical change, $△H=△U+△n_gRT$
where, $△n_g$= No. of gaseous moles of product - Reactant
So, For $△H=△U$ or $△H=△E$, $△n_g$ has to zero.
In option (A)
$△n_g=2−2=0$
Therefore, △H = △E.

So, the correct option is (A): H2(g) + Br2(g) $→$ 2HBr(g)