Cracking reaction

C₂H₆ + H₂ → 2CH₄

heats up at

Explanation and Calculation:

• Bond Dissociation Energies (approximate values):
  • C-H bond inC2H6 : 413 kcal/mol
  • C-C bond in C2H6 : 348 kcal/mol
  • H-H bond: 436 kcal/mol
  • C-H bond in CH₄ : 413 kcal/mol
• Total Bond Dissociation Energy:
  • For C2H6 :
    • 1 x 348 + 6 x 413 = 2826 kcal
  • For H₂ :
    • 1 x 436 = 436 kcal
  • Total energy to break bonds:
    • 3262 kcal
• Total Bond Formation Energy:
  • For 2 CH₄ :
    • 2 x (4 x 413) = 3304 kcal
  • Total energy to form bonds:
    • 3304 kcal
• Heat Change ( \Delta H ) for the reaction:
  • \(\Delta H = \text{Energy of bonds broken} - \text{Energy of bonds formed} \\ \Delta H = 3262 \text{ kcal} - 3304 \text{ kcal} = -42 \text{ kcal}\)
  • Convert to calories:
    • \(\Delta H = -42000 \text{ cal}\)

Conclusion:

The heat change for this reaction is closest to 41745 cal