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Stabilities of alkanes can be compared b...

Stabilities of alkanes can be compared by converting these compounds to a common product and comparing the amount of the heat given off. One possibility would be to measure the heat of combustion from converting alkenes to `CO_(2)` and `H_(2)O` . The heats of combustion are of large values and measuring small difference in these large numbers is difficult. Alkene of the lowest heat of combustion among isomeric alkenes is of the lowest energy and is most stable.
Th stability of alkenes is often compared by meansuring the ehat of hydrogenation `9` heat given off, `Delta H_(h)^(@)` during catalytic hydrogenation. The heat of hydrogenation is in smal number, which provides more accurate energy difference.
For a compound containing more than one double bond, `Delta_(h)^(@)` is the sum of heat of hydrogenation of individual double bonds. For non `-` conjugated diens, this additive relatioship is found to hold. For conjugated dienes, however, the measured value is slightly lower than expected. Cumulated dienes, which are even less stable than non `-` conjugated dienes.
The more stable is the alkene, lower is the heat of combustion and heat of hydrogenation. More highly substituted double bonds are usually more stable. In case of cyclokanes, compounds having higher angle strin are less stable.
Which statement is false `?`

A

Hydrogenation is an exothermic reaction.

B

Heat of hydrogenation is better than heat of combustion for meansuring the stabilities of alkenes.

C

Among the isomers alkene, the most stable alkene has the
lowest heat of hydrogenation and the highest heat of combustion.

D

Among the isomeric alkenes, the most stable alkenne has the lowest value of heat of hydrogenation and heat of combustion

Text Solution

Verified by Experts

The correct Answer is:
C
Statement is itself an explanation.
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Stabilities of alkanes can be compared by converting these compounds to a common product and comparing the amount of the heat given off. One possibility would be to measure the heat of combustion from converting alkenes to CO_(2) and H_(2)O . The heats of combustion are of large values and measuring small difference in these large numbers is difficult. Alkene of the lowest heat of combustion among isomeric alkenes is of the lowest energy and is most stable. Th stability of alkenes is often compared by meansuring the ehat of hydrogenation 9 heat given off, Delta H_(h)^(@) during catalytic hydrogenation. The heat of hydrogenation is in smal number, which provides more accurate energy difference. For a compound containing more than one double bond, Delta_(h)^(@) is the sum of heat of hydrogenation of individual double bonds. For non - conjugated diens, this additive relatioship is found to hold. For conjugated dienes, however, the measured value is slightly lower than expected. Cumulated dienes, which are even less stable than non - conjugated dienes. The more stable is the alkene, lower is the heat of combustion and heat of hydrogenation. More highly substituted double bonds are usually more stable. In case of cyclokanes, compounds having higher angle strin are less stable. In which of the following is Delta H^_(h)^(@) the maximum ?

Stabilities of alkanes can be compared by converting these compounds to a common product and comparing the amount of the heat given off. One possiblitiy would be to measure the heat of combustion from converting alkenes to xo_(2) and H_(2)O . The heats of combustion are of large values and measuring small difference in these large numbers is difficult. Alkene of the lowest heat of combustion among isomeric alkenes is of the lowest energy and is most stable. Th stability of alkenes is often compared by meansuring the ehat of hydrogenation 9 heat given off, Delta H_(h)^(@) during catalytic hydrogenation. The heat of hydrogenation is in smal number, which provides more accurate energy difference. For a compound containing more than one double bond, Delta_(h)^(@) is the sum of heat of hydrogenation of individual double bonds. For non - conjugated diens, this additive relatioship is found to hold. For conjugated dienes, however, the measured value is slightly lower than expected. Cumulated dienes, which are even less stable than non - conjugated dienes. The more stable is the alkene, lower is the heat of combustion and heat of hydrogenation. More highly substituted double bonds are usually more stable. In case of cyclokanes, compounds having higher angle strin are less stable. If the heat of hydrogenation of cyclooctene is about 23 k cal mo^(-1) , what would be the probable DeltaH_(b) or 1,3,5,7- cyclooctatetraene ?

Knowledge Check

  • Which one of the following has lowest heat of combustion?

    A
    B
    C
    D

  • Which of the following has the lowest heat of combustion?

    A
    B
    C
    D

  • Which one of the following has the smallest heat of combustion ?

    A
    B
    C
    D

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    Stabilities of alkanes can be compared by converting these compounds to a common product and comparing the amount of the heat given off. One possiblitiy would be to measure the heat of combustion from converting alkenes to xo_(2) and H_(2)O . The heats of combustion are of large values and measuring small difference in these large numbers is difficult. Alkene of the lowest heat of combustion among isomeric alkenes is of the lowest energy and is most stable. Th stability of alkenes is often compared by meansuring the ehat of hydrogenation 9 heat given off, Delta H_(h)^(@) during catalytic hydrogenation. The heat of hydrogenation is in smal number, which provides more accurate energy difference. For a compound containing more than one double bond, Delta_(h)^(@) is the sum of heat of hydrogenation of individual double bonds. For non - conjugated diens, this additive relatioship is found to hold. For conjugated dienes, however, the measured value is slightly lower than expected. Cumulated dienes, which are even less stable than non - conjugated dienes. The more stable is the alkene, lower is the heat of combustion and heat of hydrogenation. More highly substituted double bonds are usually more stable. In case of cyclokanes, compounds having higher angle strin are less stable. The wrong option among the following statements is :

    Stabilities of alkanes can be compared by converting these compounds to a common product and comparing the amount of the heat given off. One possiblitiy would be to measure the heat of combustion from converting alkenes to xo_(2) and H_(2)O . The heats of combustion are of large values and measuring small difference in these large numbers is difficult. Alkene of the lowest heat of combustion among isomeric alkenes is of the lowest energy and is most stable. Th stability of alkenes is often compared by meansuring the ehat of hydrogenation 9 heat given off, Delta H_(h)^(@) during catalytic hydrogenation. The heat of hydrogenation is in smal number, which provides more accurate energy difference. For a compound containing more than one double bond, Delta_(h)^(@) is the sum of heat of hydrogenation of individual double bonds. For non - conjugated diens, this additive relatioship is found to hold. For conjugated dienes, however, the measured value is slightly lower than expected. Cumulated dienes, which are even less stable than non - conjugated dienes. The more stable is the alkene, lower is the heat of combustion and heat of hydrogenation. More highly substituted double bonds are usually more stable. In case of cyclokanes, compounds having higher angle strin are less stable. Arrange the following compounds according to their increasing heat of combustion. I. 1- Butene II. cis -2- Butene III. trans -2- Butene IV. 2- Methyl propene

    The gas with the highest heat of combustion is :

    Write shot notes on the Heat of combustion.

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