NEET Chemistry: Thermochemistry questions with solutions

Q1. \( \boldsymbol{S}+\frac{\mathbf{3}}{\mathbf{2}} \boldsymbol{O}_{2} \rightarrow \boldsymbol{S} \boldsymbol{O}_{3}+\mathbf{2} \boldsymbol{x} \) kcal \( \boldsymbol{S O}_{2}+\frac{1}{2} \boldsymbol{O}_{2} \rightarrow \boldsymbol{S} \boldsymbol{O}_{3}+\boldsymbol{y} \) kcal The heat of formation of \( S O_{2} \) is:

1. \( y-2 x \)
2. \( 2 x+y \)
3. \( x+y \)
4. \( 2 x / y \)

Answer: \( y-2 x \)

The heat of formation of SO2 is the enthalpy change for S + O2 → SO2. By reversing the first equation and adding it to the second, SO3 cancels and the net reaction becomes S + O2 → SO2. The corresponding heat change is y - 2x.