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Anonymous asked in Science & MathematicsChemistry · 2 months ago

For a particular isomer of C8H18, the combustion reaction produces 5113.3 kJ of heat per mole of C8H18(g)?

For a particular isomer of C8H18,

the combustion reaction produces 5113.3 kJ of heat per mole of C8H18(g)

consumed, under standard conditions.

C8H18(g)+252O2(g)⟶8CO2(g)+9H2O(g)ΔH∘rxn=−5113.3 kJ/mol

What is the standard enthalpy of formation of this isomer of C8H18(g)

2 Answers

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  • 2 months ago

    First, the given equation must be written correctly:

    C8H18(g) + 25/2 O2(g) → 8 CO2(g) + 9 H2O(g)  ΔH = −5113.3 kJ

    Let z be the standard enthalpy of formation (in kJ/mol) to be found:

    Then products - reactants (all units in kJ):

    (8 × −393.509) + (9 × −241.818) - z - (25/2 × 0) = −5113.3 kJ

    Solve for z algebraically:

    z = −211.1 kJ/mol

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  • david
    Lv 7
    2 months ago

    I assume you have a table in your book somewhere with some std enthalpy values  ... I do not.

     Rule is that Std enthalpy of formation is the enthalpy of formation from elements, not other compounds

      look up  CO2  and H2O  in the table === tthese are values per mole

    Formation  means formation from the elements

      8C  +  9H2  -->  C8H18

    notice C8H18 is a product  so formation, not combustion of this compound

      +5113.3 - 8X(value for CO2) - 9X(value for H20)

     ... just look up those values and use a calculator

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