Question Video: Calculating the Carbon–Iodine Bond Energy in Iodination of Ethene | Nagwa Question Video: Calculating the Carbon–Iodine Bond Energy in Iodination of Ethene | Nagwa

# Question Video: Calculating the Carbon–Iodine Bond Energy in Iodination of Ethene Chemistry • First Year of Secondary School

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Ethene and iodine react to form 1,2-diiodoethane. The equation for this reaction is shown. The total energy change per mole of ethene reacted is −24 kJ/mol per mole. The energies of selected bonds in the reactants and products are given in the table. Calculate, to the nearest kilojoules per mole, the bond energy of the C–I bond.

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### Video Transcript

Ethene and iodine react to form 1,2-diiodoethane. The equation for this reaction is shown. The total energy change per mole of ethene reacted is negative 24 kilojoules per mole. The energies of selected bonds in the reactants and products are given in the table. Calculate, to the nearest kilojoules per mole, the bond energy of the CI bond.

Bond energy is the average amount of energy required to break a bond in one mole of gaseous particles. To answer this question, we need to determine the bond energy of a carbon-iodine single bond. We’ve been given a reaction equation and the bond energies of several types of bonds involved in the reaction. We’ve also been told that the total energy change per mole of ethene reacted is negative 24 kilojoules per mole. This value is the change in bond enthalpy represented with the symbol Δ𝐻. The negative sign tells us that this reaction is exothermic, meaning that energy is released to the surroundings during the reaction.

The change in bond enthalpy of a reaction can be calculated by summing the bond energies of the bonds broken during the reaction and subtracting the sum of the bond energies of the bonds that are formed. If we look at the reaction equation, we can see that a carbon-carbon double bond and an iodine-iodine single bond are broken during the reaction. So the sum of the bond energies of the bonds that are broken is 602 kilojoules per mole plus 148 kilojoules per mole. This gives us a value of 750 kilojoules per mole. We can go ahead and substitute this value along with the change in bond enthalpy into the equation.

During the reaction, one carbon-carbon single bond and two carbon-iodine single bonds are formed. So the sum of the bond energies of the bonds formed during the reaction is equal to 346 kilojoules per mole plus two times the bond energy of the carbon-iodine single bond, which we need to determine. We can substitute the sum of the bond energies of the bonds formed into the equation. We can begin to solve for the bond energy of the carbon-iodine bond by distributing the negative sign inside of the parentheses. Then we can subtract 346 kilojoules per mole from 750 kilojoules per mole, giving us 404 kilojoules per mole.

Subtracting 404 kilojoules per mole from both sides of the equation gives us negative 428 kilojoules per mole equals negative two times the carbon iodine bond energy. Dividing both sides of the equation by negative two gives us the bond energy of the carbon-iodine bond, which is 214 kilojoules per mole. So to the nearest kilojoules per mole, we have determined that the bond energy of the carbon-iodine single bond is 214 kilojoules per mole.

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