1. Tardigrade
  2. Question
  3. Chemistry
  4. Using the data provided, calculate the multiple bond energy ( textk textJ textm texto ( textl)- 1) of a textC≡ textC bond in textC2 textH2 . That energy is (take the bond energy of a textC- textH bond as 350 textk textJ textm texto textl- 1 ) 2 textC( texts) arrow 2 textC( textg ; ) Δ textH=1410 textk textJ textm texto textl- 1 ( textH)2( textg) arrow 2 textH(. textg): Δ textH=330 textk textJ textm texto textl- 1 2 textC ( texts) + ( textH)2 ( textq) arrow ( textC)2 ( textH)2 text; textΔH = 225 ( textkJmol)- 1

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Q. Using the data provided, calculate the multiple bond energy $\left(\text{k} \text{J} \, \text{m} \text{o} \left(\text{l}\right)^{- 1}\right)$ of a $\text{C}\equiv \text{C}$ bond in $\text{C}_{2}\text{H}_{2}$ . That energy is (take the bond energy of a $\text{C}-\text{H}$ bond as $350 \, \text{k}\text{J} \, \text{m}\text{o}\text{l}^{- 1}$ )
$2\text{C}\left(\text{s}\right) \rightarrow 2\text{C}\left(\text{g ; }\right)$ $\Delta \text{H}=1410 \, \text{k}\text{J} \, \text{m}\text{o}\text{l}^{- 1}$
$\left(\text{H}\right)_{2}\left(\text{g}\right) \rightarrow 2\text{H}\left(\right.\text{g}) :$ $\Delta \text{H}=330 \, \text{k}\text{J} \, \text{m}\text{o}\text{l}^{- 1}$
$2 \text{C} \left(\text{s}\right) + \left(\text{H}\right)_{2} \left(\text{q}\right) \rightarrow \left(\text{C}\right)_{2} \left(\text{H}\right)_{2} \, \, \, \text{;} \, \, \text{ΔH} = 225 \, \left(\text{kJmol}\right)^{- 1}$

NTA AbhyasNTA Abhyas 2022

Solution:

(i) $2\text{C}\left(\text{s}\right)+\left(\text{H}\right)_{2}\left(\text{g}\right) \rightarrow \text{H}-\text{C}\equiv \text{C}-\text{H}\left(\right.\text{g}\left.\right)$
$\Delta \text{H}=225 \, \text{k}\text{J} \, \text{m}\text{o}\text{l}^{- 1}$
(ii) $2\text{C}\left(\text{s}\right) \rightarrow 2\text{C}\left(\right.\text{g}\left.\right)$

$\Delta \text{H}_{1}=1410 \, \text{K}\text{J} \, \text{m}\text{o}\text{l}^{- 1}$
$\left(\text{i} \text{i} \text{i}\right) \, \left(\text{H}\right)_{2}\left(\right.\text{g}\left.\right) \rightarrow 2\text{H}\left(\right.\text{g}\left.\right)$
$\Delta \text{H}_{2}=330 \, \text{K}\text{J} \, \text{m}\text{o}\text{l}^{- 1}$
From equation (i) :
$225=\left(\Delta \left(\text{H}\right)_{1} + \Delta \left(\text{H}\right)_{2}\right)-\left[\right. \, 2\Delta \left(\text{H}\right)_{\text{C} - \text{H}}+\Delta \left(\text{H}\right)_{\text{C} \equiv \text{C}}\left]\right.$
$225=\left[ \, 1410 + 330\right]+\left(2 \times 350\right)+\Delta \left(\text{H}\right)_{\text{C} \equiv \text{C}} \, \left]\right. \, $
$225=1040-\Delta \text{H}_{\text{C} \equiv \text{C}}$
$\Delta \text{H}_{\text{C} \equiv \text{C}}=1040-225=815 \, \text{K}\text{J} \, \text{m}\text{o}\text{l}^{- 1}$