Question

Consider the reactions: $ C(s)+2{{H}_{2}}(g)\xrightarrow{{}}C{{H}_{4}}(g); $ $ \Delta H=-x\,kcal $ $ C(g)+4H(g)\xrightarrow{{}}C{{H}_{4}}(g); $ $ \Delta H=-\,y\,kcal $ $ C{{H}_{4}}(g)\xrightarrow{{}}C{{H}_{3}}(g)+H(g); $ $ \Delta H=+\,z\,kcal $ The bond energy of C?H bond is:

• A. $ \text{y}\,\text{kcal}\,\text{mo}{{\text{l}}^{-1}} $
• B. $ z\,\text{kcal}\,\text{mo}{{\text{l}}^{-1}} $
• C. $ \frac{x}{4}\,\text{kcal}\,\text{mo}{{\text{l}}^{-1}} $
• D. $ \frac{y}{2}\,\text{kcal}\,\text{mo}{{\text{l}}^{-1}} $

Answer 1

Answer: (B)

$ C{{H}_{4}}(g)\xrightarrow{{}}C{{H}_{3}}(g)+H(g); $ $ \Delta H=+z\,kcal $ In this reaction, one C?H bond is breaking hence, $ \Delta H $ represent the bond dissociation energy of C?H bond. Hence C?H bond energy is z kcal.