Chemical Thermodynamics Question 184
Question: The enthalpy of combustion at 25°C of H2, cyclohexane $(C_6H _{12}) $and cyclohexene $(C_6H _{10})$ are -241, -3920 and -800 KJ / mole respectively. The heat of hydrogenation of cyclohexene is [BHU 2005]
Options:
A) - 121 KJ / mole
B) + 121 KJ / mole
C) - 242 KJ / mole
D) + 242 KJ / mole
Show Answer
Answer:
Correct Answer: A
Solution:
(i) $ H_2+\frac{1}{2}O_2\to H_2O,\Delta H=-241,kJ $ (ii) $ C_6H_{10}+\frac{17}{2}O_2\to 6CO_2+5H_2O,,\Delta H=-3800,kJ $ (iii) $ C_6H_{12}+9O_2\to 6CO_2+6H_2O,\Delta H=-3920,kJ $
$ C_6H_{10}+H_2\to C_6H_{12} $ Eq. (i) + Eq. (ii) - Eq. (iii) $ \Delta H=-241-3800-(-3920) $
$ =-4041+3920=-121,kJ $
