11Oye Talwar Machhli [3][3], Tell here whether the answer is correct or not.
Compute the heat of formation of liquid methyl alchohol in kilo joule per mole using the following data. Heat of vaporisation of liquid methyl alcohol=38 kJ/mol. Heat of formation of gaseous atoms from the elements in their standard states: H - 218 kJ/mol, O - 249 kJ/mol.
Average bond energies: C-H, 415 kJ/mol; C-O, 356 kJ/mol and O-H, 463 kJ/mol.
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5 Answers
11CH3OH (l)--->CH3OH ΔH = 38 kJ/mol
1/2H2(g)------------->H(g) ΔH = 218 kJ/mol
C(graphite)-->C(g) ΔH = 715 kj/mol
1/2 O2---------->O(g) ΔH = 249 kJ/mol
CH(g)---------------> C(g) +H(g) ΔH= 415kJ/mol
C-O(g)---------->C(g) + O(g) ΔH= 356kJ/mol
O-H(g)--------------->O(g) + H(g) ΔH=463kJ/mol
For the calculation of ΔHf of CH3OH, the thermochemical equation is written as
C(s) + 2H2 +1/2 O2(g)----->CH3OH, ΔH=?-----(a)
On th basis of bond enthalpy concept,
ΔH = - {sum of bond enthalpy of all bonds of products - sum of bond enthalpies of all bonds of reactants}
ΔH = {(3 x EC-H + EC-O + EO-H) - (EC(s)----->C(g)+ E1/2 H-H(g) + E1/2O2(g)}
= - {(3 x 415 +356 +463) - (715 + 4 x 218 +249)}
ΔH = -228 kJ/mol -------- (answer of equation (a))
CH3OH (g) ------> CH3OH(l)--------- (b)
On adding two thermochemical equation (a) and (b),
ΔHf = -266kJ/mol,
Hence the answer.
11
1@Chessenthus- Tu Talwaar Machhli hai kya?? :p
@Khyati- Its absolutely right :)
11Oye Swordfish, talwar Machhli tumhara naam hai, janbhujkar anjaan mat bano [3]