1. Tardigrade
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  3. Chemistry
  4. In the reaction S+ (3/2)O2 → SO3 +2x : kJ and SO2+ (1/2)O2 → SO3+y kJ heat of formation of SO2 is

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Q. In the reaction
$S+\frac {3}{2}O_2 \to SO_3 +2x \: kJ $ and $SO_2+\frac {1}{2}O_2 \to SO_3+y\,kJ$
heat of formation of $SO_2$ is

KCETKCET 2015Thermodynamics

Solution:

Key concept After applying Hess's law on the given reactions, we can get the value of heat of formation of $SO _{2}$. Hess's law states that the amount of heat evolved or absorbed in chemical change is same whether the process takes place in one step or multiple steps.

Given, $S +\frac{3}{2} O _{2} \longrightarrow SO _{3}, \Delta H_{1}=-2 \times kJ $

$SO _{2} +\frac{1}{2} O _{2} \to SO _{3}, \Delta H_{2}=- y XJ $

$S + O _{2} \to SO _{2}, \Delta H_{3} =- z \,XJ$

From Hess's law

$\Delta H_{3}+\Delta H_{2} =\Delta H_{1} $

$-z-y =-2 x$

$ \Rightarrow z=2 x-y$