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5. Thermodynamics and thermochemistry — Chemistry STD 11 Science — Question

Rajasthan BoardEnglish MediumSTD 11 ScienceChemistry5. Thermodynamics and thermochemistry1 Mark
MCQ
Which of the reaction defines $\Delta H_f^o$ ?
  • ✓
    $\frac{1}{2}{H_2}(g) + \frac{1}{2}{F_2}(g) \to HF(g)$
  • B
    $CO(g) + \frac{1}{2}{O_2}(g) \to C{O_2}(g)$
  • C
    ${C_{{\rm{diamond}}}} + {O_2}(g) \to C{O_2}(g)$
  • D
    ${N_2}(g) + 3{H_2}(g) \to 2N{H_3}(g)$
✓

Answer

Correct option: A.
$\frac{1}{2}{H_2}(g) + \frac{1}{2}{F_2}(g) \to HF(g)$
a
The standard enthalpy of formation $\left(\Delta H _{ f }^0\right)$ is the enthalpy change during formation of $1\, mole$ of substance when its constituent elements are in their standard states.

Only $(A)$ follows the definition of $\Delta H _{ f }^0$. Therefore, $(A)$ is correct answer.

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