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Calculate the heat of combustion of eith...

Calculate the heat of combustion of eithene
`CH_(2) = CH_(2)(g) + 3O_(2)(g) rarr 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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