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The standard molar heat for formation of...

The standard molar heat for formation of ethane, carbondioxide and water are respectively, -21.1,-94.1 and -68.3 Kacal `"mol"^(-1)`. What is the standard molar heat of combustion of ethane ?

Text Solution

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`2C _(("garphite")) + 3 H _(2(s)) to C _(2) H _(6 (g)) , Delta H _(1) = 0 21.1 kcl`
`C _(("graphite")) + O _(2 (g)) to CO _(2) , Delta H _(2)= 94.1 kcal`
`H _(2(g)) + (1)/(2) O _(2)_ to H _(2) O_((l)) , Delta H _(2) =- 68.3 k cal`
The required equations is
`C _(2)H _(6 (g)) + (7)/(2) O _(2 (g)) to 2 CO _(2 (g)) + 3 H _(2 ) O _((l)) , Delta H =?`
`Delta H = 2 Delta H _(2) + 3 Delta H _(3) - Delta H _(1)`
`Delta H =2 (-94.1) + 3 (-68.3) - (-21.1) =-372 ` kcal.
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