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Standard XII
Chemistry
Difference between Internal Energy and Enthalpy
Compute the h...
Question

Compute the heat of formation of liquid methyl alcohol in kilojoules per mole using the following data.
The heat of vaporisation of liquid methyl alcohol = 38 kJ/mol.
The heats of formation of gaseous atoms from the elements in their standard states: H,218 kJ/mol; C,715 kJ/mol; O,249 kJ/mol.
Average bond energies: C−H=415 kJ/mol; C−O=365 kJ/mol; O−H=463 kJ/mol.

A
−275 kJ/mol
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B
−488 kJ/mol
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C
Zero
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D
−356 kJ/mol
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Solution

The correct option is A −275 kJ/mol
C(s)+2H2(g)+12O2(g)→CH3OH(l);ΔH=?
So, ΔHf=[ΔHC(s)→C(g)+2ΔHH−H+1/2ΔHO=O]−[3ΔHC−H+ΔHC−O+ΔHO−H+ΔHvap.CH3OH]
For reactants;
Heat of atomisation of 1 mole of C=715 kJ
Heat of atomisation of 4 moles of H=4×218 kJ
Heat of atomisation of 1 mole of O=249 kJ
For products:
Heat of formation of 3 moles of C−H bonds = −3×415 kJ
Heat of formation of 1 mole of C−O bonds = −356 kJ
Heat of formation of 1 mole of O−H bonds = −463 kJ
Heat of condenstation of 1 mole of CH3OH to liquid =−38 kJ
So, On adding, we get ΔH of formation of CH3OH(l):
ΔH=715+(4×218)+249−(3×415)−365−463−38
ΔH=−275 kJ/mol

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Q. Compute the heat of formation of liquid methyl alcohol in kilojoules per mole using the following data.
The heat of vaporisation of liquid methyl alcohol = 38 kJ/mol.
The heats of formation of gaseous atoms from the elements is their standard states: H,218 kJ/mol; C,713 kJ/mol; O,249 kJ/mol.
Average bond energies: C−H=415 kJ/mol; C−O=365 kJ/mol; O−H=463 kJ/mol.
Q. Compute the enthalpy of formation of liquid methyl alcohol in kJ mol−1, using the following data.
Enthalpy of vaporisation of liquid CH3OH=38 kJ / mol.
Enthalpy of formation of gaseous atoms from the elements in their standard states are
H→218 kJ / mol ; C→715 kJ / mol ; O→249 kJ / mol.
Average Bond energies
C−H→415 kJ / mol ; C−O→356 kJ / mol; O−H→463 kJ / mol

Q. Compute the heat of formation of liquid methyl alcohol (in kJ mol −1) using the following data. The heat of vaporisation of liquid methyl alcohol is 38 kJ mol−1.

The heat of formation of gaseous atoms from the elements in their standard states:
H= 218 kJ mol−1., C=715 kJ mol−1. , O=249 kJ mol−1.

Average bond energies:
C−H=415 kJ mol−1.
C−O=356 kJ mol−1.
O−H=463 kJ mol−1.

Q. What is the heat of formation of liquid methyl alcohol in kJ mol−1 , use the following data.
Heat of vaporization of liquid methyl alcohol = 38 kJ mol−1 .
Heat of formation of gaseous atoms from the elements in their standard states:
H=218 kJ mol−1,C=715 kJ mol−1, O=249 kJ mol−1
Average bond energies :
C−H=415 kJ mol−1 C−O=356 kJ mol−1 O−H=463 kJ mol−1
Q. What is the heat of formation of liquid methyl alcohol in kJ mol−1 , use the following data.
Heat of vaporization of liquid methyl alcohol = 38 kJ mol−1 .
Heat of formation of gaseous atoms from the elements in their standard states:
H=218 kJ mol−1,C=715 kJ mol−1, O=249 kJ mol−1
Average bond energies :
C−H=415 kJ mol−1 C−O=356 kJ mol−1 O−H=463 kJ mol−1
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