1.

When 4g of iron is burnt to ferric oxide at constant pressure, 29.28KJ of heat is evolved. What is the enthalpy of formation of ferric oxide (At wt. of Fe=56)

Answer»

`-81.98 kJ`
`-819.8 kJ`
`-40.99 kJ`
`+819.8 kJ`

SOLUTION :Given: Weight of iron burnt=4g, Heat liberated =29.28 KJ and ATOMIC weight of iron (Fe)56. We know that in ferric OXIDE `(Fe_(2)O_(3))`, 2 moles of iron or `2xx56=112`gram of iron are burnt. We also know that when 4 grams of iron are burnt, then heat liberated = 29.28 kJ, therefore when 112 grams of the iron are burnt, then heat liberated `=(29.28xx112)/(4)=-819.8 kJ`(Minus sign due to LIBERATION of heat).


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