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.
What is the standard enthalpy of formation of this isomer of C8H18(g)
- Roger the MoleLv 72 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
- davidLv 72 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