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AP EAMCET · Chemistry · Thermodynamics (C)

The atomisation enthalpy of \(\mathrm{CH}_4\) is \(1660 \mathrm{~kJ} \mathrm{~mol}^{-1}\). The \(\mathrm{C}-\mathrm{H}\) bond enthalpy of each successive step in
\(\mathrm{CH}_4 \rightarrow \mathrm{CH}_3 \rightarrow \mathrm{CH}_2 \rightarrow \mathrm{CH}\) are \(+15,+30\) and \(+45 \mathrm{~kJ} \mathrm{~mol}^{-1}\) higher than the mean bond enthalpy of \(\mathrm{CH}\) bonds, respectively. The bond enthalpy of the last \(\mathrm{C}-\mathrm{H}\) unit is

  1. A \(400 \mathrm{~kJ} \mathrm{~mol}^{-1}\)
  2. B \(325 \mathrm{~kJ} \mathrm{~mol}^{-1}\)
  3. C \(475 \mathrm{~kJ} \mathrm{~mol}^{-1}\)
  4. D \(385 \mathrm{~kJ} \mathrm{~mol}^{-1}\)
Verified Solution

Answer & Solution

Correct Answer

(B) \(325 \mathrm{~kJ} \mathrm{~mol}^{-1}\)

Step-by-step Solution

Detailed explanation

The atomisation enthalpy of \(\mathrm{CH}_4\) is \(1660 \mathrm{~kJ} \mathrm{~mol}^{-1}\). \(\mathrm{CH}_4(g) \longrightarrow \mathrm{C}(g)+4 \mathrm{H}(g) ; \quad \Delta_a H=1660 \mathrm{kJmol}^{-1}\)…