Figure out the number of reactions among the following which have `DeltaH` equal to `DeltaU`
i. `N_2 (g) + 3H_2 (g) to 2 NH_3 (g)`
ii. `2 HI (g) to H_2 (g) + I_2 (g)`
iii. `C(s) + O_2 (g) to CO_2 (g)`
iv. `2 NO_2 (g) to N_2O_4`
v. `2SO_2 (g) + O_2 (g) to 2SO_3 (g)`
vi. `CH_4 (g) + 2O_2 (g) to CO_2(g) + 2H_2O (l)`
vii. `2C_4H_10 (g) + 13O_2 (g) to 8 CO_2 (g) + 10H_2O (l)`
viii. `H_2 (g) + Br_2 (g) to 2 HBr (g) `

Answer

C

Explanation

Apply the given relationship between the change in enthalpy and the change in internal energy.
`DeltaH = DeltaU + Deltan_g RT `
Where `Delta_(n_g)` =(Number of gaseous moles of product - number of gaseous moles of reactants)
(ii) `2 HI(g) to H_2 (g) + I_2 (g)`
(iii) `C(s) + O_2(g) to CO_2 (g) `
(viii) `H_2 (g) + Br_2 (g) to 2 HBr (g) `
For reactions, ii, iii, and viii `Delta_(n_g) = 0`.
Hence,
`DeltaH = DeltaU`
Therefore, total three reaction are present that have the change in enthalpy is equal to the change in internal energy.