KCET · Chemistry · Thermodynamics (C)
Given thermochemical equation, \(2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \rightarrow 2 \mathrm{H}_{2} \mathrm{O}(l) ; \Delta H=-571.6 \mathrm{~kJ}\). Heat of decomposition of water is
- A \(-571.6 \mathrm{~kJ}\)
- B \(+571.6 \mathrm{~kJ}\)
- C \(-1143.2 \mathrm{~kJ}\)
- D \(+285.8 \mathrm{~kJ}\)
Answer & Solution
Correct Answer
(D) \(+285.8 \mathrm{~kJ}\)
Step-by-step Solution
Detailed explanation
Given
(i) \(2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O} ; \Delta \mathrm{H}=-571.6 \mathrm{~kJ}\) At \(\quad \mathrm{H}_{2} \mathrm{O}(I) \longrightarrow \mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) ; \Delta H=?\)
If reaction (i) is reversed and divided by 2 , the sign of \(\Delta H\) changes, i.e.,
\(\Delta H\) for decomposition of water
\(=+\frac{571.6}{2}=285.8 \mathrm{~kJ}\)
(i) \(2 \mathrm{H}_{2}(g)+\mathrm{O}_{2}(g) \longrightarrow 2 \mathrm{H}_{2} \mathrm{O} ; \Delta \mathrm{H}=-571.6 \mathrm{~kJ}\) At \(\quad \mathrm{H}_{2} \mathrm{O}(I) \longrightarrow \mathrm{H}_{2}(g)+\frac{1}{2} \mathrm{O}_{2}(g) ; \Delta H=?\)
If reaction (i) is reversed and divided by 2 , the sign of \(\Delta H\) changes, i.e.,
\(\Delta H\) for decomposition of water
\(=+\frac{571.6}{2}=285.8 \mathrm{~kJ}\)
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