Question

Assume each reaction is carried out in an open container.
For which reaction will ∆H = ∆E ?
(a) C(s) + 2H₂O (g) ® 2H₂ (g) + CO₂ (g)
(b) PCl₅ (g) ® PCl₃ (g) + Cl₂ (g)
(c) 2CO (g) + O₂ (g) ® 2CO₂ (g)
(d) H₂ (g) + Br₂ (g) ® 2 HBr (g)

Answer 1

$\huge\underline \mathfrak \blue{Answer}$

(d) H₂ (g) + Br₂ (g) ® 2 HBr (g)

Answer 2

Reaction for which ∆H = ∆E would be :

• We know relation between ∆H and ∆E

i.e ∆H = ∆E + ∆ngRT

• Where ∆H = Enthalpy change

∆E = Internal energy change

R = Universal gas constant

∆ng = moles of product in gaseous state - moles of reactants in gaseous state

• For ∆H = ∆E, we've to find reaction where ∆ng = 0

• In (a) reaction, ∆ng = 3 - 2 = 1

• (b), ∆ng = 2 - 1 = 1

• (c), ∆ng = 2 - 3 = -1

• (d), ∆ng = 2 - 2 = 0

• Hence, we can see that in (d) reaction ∆ng =0

• Correct option : (d) H₂ (g) + Br₂ (g) ® 2 HBr (g)