If bond energies of N≡ N, H-H and N-H bonds are 945, 437 and 389 kJ respectively, AH for the following gaseous reaction is N2+3H2 xrightarrow2NH3

Question

If bond energies of N≡ N, H-H and N-H bonds are 945, 437 and 389 kJ respectively, AH for the following gaseous reaction is N2+3H2 xrightarrow2NH3  (A)  -78 kJ  (B)  -156 kJ  (C)  -1478 kJ  (D)  +1478 kJ

Tardigrade Admin · Accepted Answer

N2+3H2 xrightarrow2NH3 For this reaction, Heat evolved =6× ( N-H bond energy) - [3 ( H-H bond energy) + ( N≡ N ) bond energy] = 6 (389) - [3 (437) + (945)] = 2334 - (1311 + 945) = 2334 - 2256 = 78 kJ ∴ Δ H=-78 kJ

Q. If bond energies of $N \equiv N,$ $H - H$ and $N - H$ bonds are 945, 437 and 389 kJ respectively, AH for the following gaseous reaction is $N_{2} + 3 H_{2} 2 N H_{3}$

$- 78 k J$

$- 156 k J$

$- 1478 k J$

$+ 1478 k J$

$N_{2} + 3 H_{2} 2 N H_{3}$ For this reaction, Heat evolved $= 6 \times$ ( $N - H$ bond energy) $-$ [3 ( $H - H$ bond energy) + ( $N \equiv N$ ) bond energy] = 6 (389) $-$ [3 (437) + (945)] = 2334 $-$ (1311 + 945) = 2334 $-$ 2256 = 78 kJ $∴$ $Δ H = - 78 k J$

Q. If bond energies of N≡N, H−H and N−H bonds are 945, 437 and 389 kJ respectively, AH for the following gaseous reaction is N2​+3H2​​2NH3​

−78kJ

−156kJ

−1478kJ

+1478kJ