The data given below are for vapour phase reactions at constant pressure- C2H6- C2H5- -H- - H-420 kJ mol-1 -C2H5- C2H4-H- - H-168 kJ mol-1The enthalpy change for the reaction for the given reaction is - 2-C2H5- C2H6-C2H4

For the reaction $A + B \to C + D Δ H = - 20 k J m o l^{- 1}$ . The activation energy of the forward reaction is $85 k J m o l^{- 1}$ . The activation energy for backward reaction is

Q. The average O-H bond energy with the help of following data is:

(1) 2 H (g) ⟶ H_{2} (g); Δ H = - 435.0 {kJ mol}^{- 1}

(2) O_{2} (g) ⟶ 2 O (g); Δ H = + 489.6 {kJ mol}^{- 1}

(3) \frac{1}{2} H_{2} (g) + \frac{1}{2} O_{2} (g) ⟶ O H; Δ H = - 42.09 {kJ mol}^{- 1}

Q. Use the bond energies to estimate

Δ H

for this reaction:

H_{2} (g) + O_{2} (g) ⟶ H_{2} O_{2} (g)

Bond

Bond energy

H - H

436 k J

{m o l}^{- 1}

O - O

142 k J

{m o l}^{- 1}

O = O

499 k J

{m o l}^{- 1}

H - O

460 k J

{m o l}^{- 1}

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The data given below are for vapour phase reactions at constant pressure.C2H6→∙C2H5+∙H; ΔH=420 kJ mol−1∙C2H5→C2H4+∙H; ΔH=168 kJ mol−1The enthalpy change for the reaction for the given reaction is :2∙C2H5→C2H6+C2H4

The correct option is C −252 kJ mol−1i) C2H6→∙C2H5+∙H;ΔH=420 kJ/molii) ∙C2H5→C2H4+∙H;ΔH=168 kJ/moliii) C2H4+∙H→∙C2H5;ΔH=−168 kJ/molAdding (i) and (iii) we get C2H6+C2H4→2∙C2H5;ΔH=420−168=252 kJmol−1So, ΔH′=−252 kJmol−1