Anonymous
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)

Relevance
• 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

• Login to reply the answers
• 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

• Login to reply the answers