Question

What is the heat of hydrogenation in a hydrogenation reaction?

Answer 1

Hint: The addition of hydrogen to any unsaturated compound to make a saturated compound in the presence of a catalyst is called Hydrogenation reaction. At the time of hydrogenation there is a need for a catalyst.

Complete answer:
- In the question it is asked what the heat of hydrogenation in a hydrogenation reaction is.
- If any compound is going to have a double or triple bond in it then they undergoes a hydrogenation reaction which means addition of hydrogen atoms to the double or triple bond and makes them to saturated compound.
- At the time of hydrogenation of alkenes or alkynes a large amount of energy is going to be released, the released energy is called heat of hydrogenation.
- The heat of hydrogenation is going to measure with $\Delta H$ .
- For exothermic reaction the heat of hydrogenation is negative and for endothermic reaction the heat of hydrogenation is a positive value.
- The heat of hydrogenation of the double bond in alkene is 602 kJ/mol.
- The heat of hydrogenation of the single bond in alkane is 346 kJ/mol.
- The heat of hydrogenation of the bond in between the hydrogen atoms is 436 kJ/mol.
- The heat of hydrogenation of the C-H bond in an alkane is 413 kJ/mol.

Note:
In an exothermic reaction the energy is going to be released that is why the value of heat of hydrogenation is negative of exothermic reaction in the presence of a catalyst and it is positive for endothermic reactions.