The heat of formation of (E)-1,3 -pentadiene is 75.8 kJ mol^-1 (18. I kcal mol ^-1 ), and that

step 1 Dear students in the given problem problem 209 209 of chapter 4 we have asked to calculate calcu

The heat of formation of (E)-1,3 -pentadiene is 75.8 kJ...

The heat of formation of $(E)-1,3$ -pentadiene is $75.8 \mathrm{~kJ} \mathrm{~mol}^{-1}$ (18. I kcal mol $^{-1}$ ), and that of 1,4 -pentadiene is $106.3 \mathrm{~kJ} \mathrm{~mol}^{-1}\left(25.4 \mathrm{kcal} \mathrm{mol}^{-1}\right)$ (a) Which alkene has the more stable arrangement of bonds? (b) Calculate the heat liberated when one mole of 1,3 pentadiene is burned. The heat of combustion of carbon is $-393.5 \mathrm{~kJ} \mathrm{~mol}^{-1}\left(-94.05\right.$ keal $\left.\mathrm{mol}^{-1}\right),$ and that of $\mathrm{H}_{2}$ is $-285.8 \mathrm{~kJ} \mathrm{~mol}^{-1}\left(-68.32 \mathrm{kcal} \mathrm{mol}^{-1}\right)$

The heat of formation of $(E)-1,3$ -pentadiene is $75.8 \mathrm{~kJ} \mathrm{~mol}^{-1}$ (18. I kcal mol $^{-1}$ ), and that of 1,4 -pentadiene is $106.3 \mathrm{~kJ} \mathrm{~mol}^{-1}\left(25.4 \mathrm{kcal} \mathrm{mol}^{-1}\right)$
(a) Which alkene has the more stable arrangement of bonds?
(b) Calculate the heat liberated when one mole of 1,3 pentadiene is burned. The heat of combustion of carbon is $-393.5 \mathrm{~kJ} \mathrm{~mol}^{-1}\left(-94.05\right.$ keal $\left.\mathrm{mol}^{-1}\right),$ and that of $\mathrm{H}_{2}$
is $-285.8 \mathrm{~kJ} \mathrm{~mol}^{-1}\left(-68.32 \mathrm{kcal} \mathrm{mol}^{-1}\right)$

Key Concepts

Heat of Combustion

The heat of combustion is the energy released as heat when a substance undergoes complete combustion with oxygen. It represents the total energy difference between the reactants and the products (typically CO2 and H2O for organic compounds), and is used to quantify the energy content of fuels and other hydrocarbons.

Conjugation in Dienes

Conjugation occurs when alternating single and double bonds allow for the delocalization of electrons across a molecule. In dienes, conjugation leads to a stabilization of the molecule by lowering its overall energy, which is often reflected in a lower heat of formation compared to nonconjugated alternatives.

Heat of Formation

The heat of formation is the enthalpy change when one mole of a compound is formed from its constituent elements in their standard states. It reflects the inherent energy content and stability of the compound; compounds with lower (or less positive) heats of formation are generally more stable because they are closer to the energy of their stable elemental forms.

Thermodynamic Stability

Thermodynamic stability refers to the relative energy levels of compounds, indicating how much energy is stored in their chemical bonds. A molecule with a lower overall energy (i.e., a lower heat of formation) is considered more stable, as it is less likely to spontaneously transform into another structure under standard conditions.

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