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Question
The standard enthalpy of combustion at 25o C of hydrogen, cyclohexene (C6H10) and cyclohexane (C6H12 ) are −241, −3800 and −3920kJ mol−1 respectively. Calculate the heat of hydrogenation of cyclohexene ( in kJ mol−1)
The standard enthalpy of combustion at 25o C of hydrogen, cyclohexene (C6H10) and cyclohexane (C6H12 ) are −241, −3800 and −3920kJ mol−1 respectively. Calculate the heat of hydrogenation of cyclohexene ( in kJ mol−1)
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Solution
The correct option is B + 121
The equation of the reaction of hydrogenation of cyclohexane:
eq. 1
C6H10+H2→C6H12 ΔH1=?
We are given that,
H2+12O2→H2OΔH2=−241 kJ/mole
C6H10+172O2→6CO2+5H2OΔH3=−3800 kJ/mole
C6H12+9O2→6CO2+6H2OΔH4=−3920 kJ/mole
The required eq. 1 can be obtained by adding eq.2 and eq.3 and subtracting eq. 4 from it.
So, for eq.1,
ΔH1=ΔH2+ΔH3−ΔH4
putting all the values,
=[−3800−241−(−3920)]kJ mol−1
=−121 kJ mol−1
hence the heat of hydrogenation of cyclohexene is =−121 kJ mol−1
The equation of the reaction of hydrogenation of cyclohexane:
eq. 1
C6H10+H2→C6H12 ΔH1=?
We are given that,
H2+12O2→H2OΔH2=−241 kJ/mole
C6H10+172O2→6CO2+5H2OΔH3=−3800 kJ/mole
C6H12+9O2→6CO2+6H2OΔH4=−3920 kJ/mole
The required eq. 1 can be obtained by adding eq.2 and eq.3 and subtracting eq. 4 from it.
So, for eq.1,
ΔH1=ΔH2+ΔH3−ΔH4
putting all the values,
=[−3800−241−(−3920)]kJ mol−1
=−121 kJ mol−1
hence the heat of hydrogenation of cyclohexene is =−121 kJ mol−1
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