Question

The heat of combustion of c2h4 c2h6 and h2 are

Answer 1

The heat of combustion of c2h4 c2h6 and h2 are - 136.8KJ

Given,

C₂h₄+H₂=C₂H₆

∆Hhydrogenation=∆Hcombustion

(C₂H₄)

+∆Hcombustion(H₂)-

∆Hcombustion(C₂H₆)

=(-1409.5)+(-285.6)-(1558.3)

=-1695.1+1558.3

=-1368kj

Answer 2

The complete question is :-

The heats of combustion of C2H4, C2H6 and H2 are−1400⋅5 kJ, −1558⋅3 kJ and −285⋅6 kJ. The heat of hydrogenation of ethene will be?

The amount of heat of hydrogenation of ethene is -136.8 kJ.

By formula we have:-

Heat of hydrogenation of ethene = Heat of combustion of ethene(C2H4) + Heat of combustion of hydrogen(H2) - Heat of combustion of ethane(C2H6)

Heat of combustion of ethene = -1400.5 kJ

Heat of combustion of ethane = -1558.3 kJ

Heat of combustion of hydrogen = -285.6 kJ

• We know heat of combustion is the amount of heat released during the combustion of specified amount of substance.
• Heat of hydrogenation is the heat or standard enthalpy of catalytic hydrogenation of alkene as it is always exothermic so energy is always released so (-) sign.

Substituting values in:-

Heat of hydrogenation of(C2H4) = Heat of combustion of(C2H4) + Heat of combustion of (H2) - Heat of combustion ofC2H6)

Heat of hydrogenation of ethene = (-1409.5) + (-285.6) -(-1558.3) kJ

Heat of hydrogenation of ethene = -1695.1 +1558.3 kJ

Heat of hydrogenation of ethene = -136.8 kJ

The negative sign indicates there is release in energy and reaction is exothermic in nature.

Hence heat of hydrogenation of ethene is -136.8 kJ.