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`)

Options

A. `–81.98 kJ `
B. `–819.8 kJ `
C. `–40.99 kJ `
D. `+819.8 kJ `

Answer

B

Explanation

`2Fe+3/2 O_(2) to Fe_(2) O _(3)`
i.g Fe reacts to give `=29.28 kJ`
` 2xx56 g ` Fe reacts to give `=(2928)/(4)xx2xx56=819.8 kJ`
`DeltaH =-819. 9kJ`