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Chemistry · Enthalpies of bond dissociation, combustion, formation, atomization, sublimation, phase transition, hydration, ionization and solution

Which of the following equations corresponds to the definition of enthalpy of fo

Which of the following equations corresponds to the definition of enthalpy of formation at \( 298 K ? \)

  • A. \( C(\text {graphite})+2 H_{2}(g)+1 / 2 O_{2}(l) \rightarrow C H_{3} O H(g) \)
  • B. \( C(\text { diamond })+2 H_{2}(g)+1 / 2 O_{2}(g) \rightarrow C H_{3} O H(l) \)
  • C. \( 2 C(\text { graphite })+4 H_{2}(g)+O_{2}(g) \quad \rightarrow 2 C H_{3} O H(l) \)
  • D. \( C(\text {graphite})+2 H_{2}(g)+1 / 2 O_{2}(g) \rightarrow C H_{3} O H(l) \)

Step-by-step solution

The standard enthalpy of formation is defined as the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states. For methanol (CH3OH) at 298 K, the standard state of carbon is graphite, hydrogen is H2(g), oxygen is O2(g), and the product is CH3OH(l). Option D meets all these criteria: it uses graphite, H2(g), O2(g), and produces exactly one mole of liquid methanol.
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