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Question
Write an application of Hess’s law.
Solution 1
The Hess's law has been useful to calculate the enthalpy changes for the reactions with their enthalpies being not known experimentally.
Solution 2
- It helps in calculating the enthalpies of formation of those compounds which cannot be determined experimentally.
- It helps in determining the enthalpy of allotropic transformation like C(graphite)→C(diamond)
- It helps in calculating the enthalpy of hydration.
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\[\begin{array}{cc}
\phantom{}\ce{H}\phantom{...}\ce{H}\phantom{...................}\ce{H}\phantom{...}\ce{H}\phantom{....}\\
\phantom{.}|\phantom{....}|\phantom{....................}|\phantom{....}|\phantom{.....}\\
\ce{C = C + H - H -> H - C - C - H}\\
\phantom{.}|\phantom{....}|\phantom{....................}|\phantom{....}|\phantom{.....}\\
\phantom{}\ce{H}\phantom{...}\ce{H}\phantom{...................}\ce{H}\phantom{...}\ce{H}\phantom{....}
\end{array}\]
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