Question

Consider the following two reactions :
(i) Propene $+ H_2 \to$ Propane ; $\Delta H_1$
(ii) Cyclopropane $+ H_2$ Propane ; $\Delta H_2$
Then, $\Delta H_2 - \Delta H_1$ will be

• A. $0$
• B. $2BE_{C-C} - BE_{C = C}$
• C. $BE_{C = C}$
• D. $2BE_{C = C} - BE_{C - C}$

Answer 1

Answer: (B)

$CH_3 - CH = CH_2 + H_2 \to CH_3 - CH_2 - CH_3$;
$\Delta H_1= (BE_{C = C)} +BE_{H-H}) -(2BE_{C - H} + BE_{C -C})$

$\Delta H_2 = (BE_{C— C} + BE_{H — H}) - (2 \times BE_{C— H})$
$\Delta H_2-\Delta H_1 = 2BE_{C— C} - BE_{C = C}$