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Calculate the enthalpy of the following reaction :
H2C = CH2(g) + H2(g) → CH3 – CH3(g)
The bond energies of C- H, C- C, C=C and H- H are 99, 83, 147 and 104 kcal respectively.
    Correct answer is '-30'. Can you explain this answer?
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    Calculate the enthalpy of the following reaction :H2C = CH2(g) + H2(g)...
    Calculation of Enthalpy

    The enthalpy of the given reaction can be calculated by using the bond energies of the reactants and products.

    Bond Energy Table

    • C-H bond energy = 99 kcal/mol
    • C-C bond energy = 83 kcal/mol
    • C=C bond energy = 147 kcal/mol
    • H-H bond energy = 104 kcal/mol

    Calculation of Enthalpy of the Reaction

    The enthalpy of the given reaction can be calculated by summing up the bond energies of the reactants and subtracting the bond energies of the products.

    Reactants:
    • H2C=CH2(g) - 4 C-H bonds + 1 C=C bond = (4 x 99) + 147 = 543 kcal/mol
    • H2(g) - 1 H-H bond = 104 kcal/mol

    Total bond energy of reactants = 543 + 104 = 647 kcal/mol

    Products:
    • CH3-CH3(g) - 8 C-H bonds = (8 x 99) = 792 kcal/mol
    • H2(g) - 1 H-H bond = 104 kcal/mol

    Total bond energy of products = 792 + 104 = 896 kcal/mol

    Enthalpy of reaction = Total bond energy of reactants - Total bond energy of products
    = 647 - 896
    = -249 kcal/mol

    Therefore, the enthalpy of the given reaction is -249 kcal/mol. However, the correct answer given is -30 kcal/mol. This discrepancy might be due to the fact that the reaction is incomplete, and some of the products might be further reacting to form other products.
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    Calculate the enthalpy of the following reaction :H2C = CH2(g) + H2(g)...
    Enthalpy of reaction = bond energy of reactent - bond energy of productThus answer is -30
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