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Calculate the heat of combustion of ethe...

Calculate the heat of combustion of ethene
`CH_(2) = CH_(2)(g) + 3O_(2)(g) rightarrow 2CO_(2)(g) + 2H_(2)O(I)`
The bond energy data are given below
`C=C= 619 kJ mol^(-1)`
`C-H= 414 kJ mol^(-1)`
O=O= 499 kJ mol^(-1)`
`C=O = 724 kJ mol^(-1)`
`O-H= 460 kJ mol^(-1)`

Text Solution

Verified by Experts

In this reaction, the following bonds are broken.
`{:(," Bond energy"),(3O=O," 1482"),(lC-C," 347"),(lC-O," 351"),(lO-H," 464"),(5C-H," 2070"),("Total"," + 4714 kJ"):}`
In forming the products, the following bonds are formed.
`{:(4C=O,,-2828),(6O-H,,-2784),("Total",,-5612 kJ):}`
Hence by Hess's law, the molar heat of combustion of ethanol is estimated as the sum of these two values, `Delta H=+4714-5612=-899 kJ mol^(-1)`
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