Question

\[\ce{S + 3/2O2 -> SO3 +2{x} kcal}\] .........(i)

\[\ce{SO2 + 1/2O2 -> SO3 + {y} kcal}\] .......(ii)

The heat of formation of SO₂ is ____________.

Options

• 2x − y

• 2x + y

• x + y

• y − 2x

Answer 1

\[\ce{S + 3/2O2 -> SO3 +2{x} kcal}\] .........(i)

\[\ce{SO2 + 1/2O2 -> SO3 + {y} kcal}\] .......(ii)

The heat of formation of SO₂ is y − 2x.

Explanation:

Reversing Equation (ii), we get,

\[\ce{SO3 -> SO2 + 1/2O2}\]; ΔH = y kcal .....(iii)

Adding equation (i) and (iii)

\[\ce{S + 3/2O2 -> SO3}\]; ΔH = −2x kcal

\[\ce{SO3 -> SO2 + 1/2O2}\]; ΔH = y kcal
_________________________________________

\[\ce{S + O2 -> SO2}\]; ΔH = (y − 2x kcal)