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Hess's law of heat of summatiion is bas...

Hess's law of heat of summatiion is based on law of conservation of energy. It has found significance in deriving heats of many reactions which either do not take place or if take place, than other side reactions also accompany it. For example heat of reaction for `C+(1)/(2)O_(2) rarr CO` can not be studied directly as it occurs with simultaneous reaction of oxidation of `CO` to `CO_(2)` . Bond energy is referred as heat enthalpy when a bond is broken to produce isolated gaseous atoms. In case of breaking up of bonds between unlike atoms `e.g., C-H` bond in `CH_(4)` , bond energy is referred as avarage bond energy as four `C-H` bonds are broken up.
Which of the following statements are correct ?
`(1)` The dissociation of a ond is always endothermic
`(2)` The formation of a bond is always exothermic.
`(3)` Heat of formation of an atom `=1//2xx` bond energy like atoms covalent bond.
`(4)` The heat enthalpy change in a chemical reaction is equal but opposite to the heat enthalpy if reaction is reversed.
`(5)` Hess's law can be verified experimentally.

A

`1,2,3,4`

B

`1,2,3,4,5`

C

`2,3,4,5`

D

`3,4,5`

Text Solution

Verified by Experts

The correct Answer is:
a
Hess's law can not be verified experimentally.
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Hess's law of heat of summatiion is based on law of conservation of energy. It has found significance in deriving heats of many reactions which either do not take place or if take place, than other side reactions also accompany it. For example heat of reaction for C+(1)/(2)O_(2) rarr CO can not be studied directly as it occurs with simultaneous reaction of oxidation of CO to CO_(2) . Bond energy is referred as heat enthalpy when a bond is broken to produce isolated gaseous atoms. In case of breaking up of bonds between unlike atoms e.g., C-H bond in CH_(4) , bond energy is referred as avarage bond energy as four C-H bonds are broken up. The heat of fusion for water is +1.44kcal . The heat requried to change 27g ice at 0^(@)C to water is :

Hess's law of heat of summatiion is based on law of conservation of energy. It has found significance in deriving heats of many reactions which either do not take place or if take place, than other side reactions also accompany it. For example heat of reaction for C+(1)/(2)O_(2) rarr CO can not be studied directly as it occurs with simultaneous reaction of oxidation of CO to CO_(2) . Bond energy is referred as heat enthalpy when a bond is broken to produce isolated gaseous atoms. In case of breaking up of bonds between unlike atoms e.g., C-H bond in CH_(4) , bond energy is referred as avarage bond energy as four C-H bonds are broken up. Heat of dissociation of CH_(4) and C_(2)H_(6) are 360 and 620kcal mol^(-1) . The C-C bond energy would be :

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Hess's Law and Heat of reactions