What Is the Value Of $\Delta H ^ { \circ } \text { in } \mathrm { kcal } / \mathrm { mol }$

question 19

Multiple Choice

What is the value of $\Delta H ^ { \circ } \text { in } \mathrm { kcal } / \mathrm { mol }$ for the reaction shown below?
$\left( \mathrm { CH } _ { 3 } \right) _ { 3 } \mathrm { C } - \mathrm { H } + \mathrm { Cl } - \mathrm { Cl } \rightarrow \left( \mathrm { CH } _ { 3 } \right) _ { 3 } \mathrm { C } - \mathrm { Cl } + \mathrm { H } - \mathrm { Cl }$
Bond energies are:
$\begin{array} { l } \quad \left( \mathrm { CH } _ { 3 } \right) 3 \mathrm { C } - \mathrm { H } = 91 \mathrm { kcal } / \mathrm { mol } \\\left( \mathrm { CH } _ { 3 } \right) 3 \mathrm { C } - \mathrm { Cl } = 78.5 \mathrm { kcal } / \mathrm { mol } \\\mathrm { Cl } - \mathrm { Cl } = 58 \mathrm { kcal } / \mathrm { mol } \\\mathrm { H } - \mathrm { Cl } = 103 \mathrm { kcal } / \mathrm { mol }\end{array}$

• A) +32.5
• B) -57.5
• C) -32.5
• D) +57.5
• E) -8.5

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