Question

The standard enthalpy of combustion at ${25^{{}^0}}C$of hydrogen, cyclohexene $\left( {{C_6}{H_{10}}} \right)$ and cyclohexane $\left( {{C_6}{H_{12}}} \right)$ are -241, -3800 and -3920 kJ/mole respectively. Calculate the heat of hydrogenation of cyclohexene.
A. -111kj/mol
B. -121kj/mol
C. -118kj/mol
d. -128kj/mol

Answer 1

Hint- To solve this question, we use the basic theory related to heat combustion. As we know very highly-temperature exothermic redox chemical reaction between a fuel (the reductant) and an oxidant, is a combustion in which large amounts of heat and light energy are released. In reaction is known as rapid combustion.

Complete step-by-step answer:
About Enthalpy:
Enthalpy is a capacity to reflect to do non-mechanical work and also reflect the capacity to release heat. It is a thermodynamic property. Enthalpy is the sum of the internal energy of a system added to the product of the pressure and its volume. Usually an Enthalpy is denoted as H; and some specific enthalpy denoted as h. the joule, calorie, or BTU (British Thermal Unit) are Common units used to express enthalpy
Enthalpy Formulas used: - H = E + PV
where H denotes enthalpy, E is internal energy of the system, P denotes pressure, and V represent volume.
Now,
d H = T d S + P d V
The required reaction is
${C_6}{H_{10}} + {H_2} \to {C_6}{H_{12,}}\Delta {H_1} = ?$ … (1)
Let us write the given facts
${H_2}$+$\dfrac{1}{2}{O_2} \to$ ${H_2}O$
$\Delta {H_2}$=-241kJ/mole …. (2)

${C_6}{H_{10}}$+$\dfrac{{17}}{2}{O_2}$ $\to$ $6C{O_2}$+$5{H_2}O$
$\Delta {H_3}$=-300kJ/mole ….. (3)

${C_6}{H_{12}}$ $+ 9{O_2}$ $\to 6C{O_2} + 6{H_2}O$
$\Delta {H_4}$=-3920kJ/mole …. (4)

The required reaction (1) can be obtained by adding equations (2) and (3), and subtracting (4) from the sum of (2) and (3).
${C_6}{H_{10}} + {H_2} \to {C_6}{H_{12}}$
$\Delta {H_1}$=$\left( {\Delta {H_2} + \Delta {H_3}} \right) - \Delta {H_4}$
= [-241+(-3800)] – (-3920)
= (-241-3800) – (-3920)
= -4041+3920=-121Kj/ mole
Therefore, the heat of hydrogenation of cyclohexene is -121kJ/mol.
Thus, option (B) is the correct answer.

Note- Always remember an organic fuel Combustion in air is always exothermic it is because the double bond in oxygen $\left( {{O_2}} \right)$ is much weaker than other double bonds in the form of campfires and bonfires, combustion reaction was the first controlled chemical reaction discovered by humans Combustion is used to destroy many wastes, both non hazardous and hazardous etc.