Chemistry - Thermochemistry Question with Solution | TestHub
Consider the following isomerization process:
CH2=CH-CH2-CH=CH2(g) → CH2=CH-CH=CH-CH3(g)
Which of the following statement(s) is/are true regarding this process? (one or more than one correct)
Options:(select one or more)
Answer:
Solution:
The reactant is 1,4-pentadiene, which contains isolated double bonds. The product is 1,3-pentadiene, which is conjugated and thus more stable due to its resonance energy.
Therefore, the isomerization is exothermic, making (a) true. The magnitude of its Δ H equals the resonance enthalpy of the product, which represents the energy lowering due to conjugation, making (b) true.
A more stable isomer releases less heat when burned to form the same products. Consequently, the magnitude of the enthalpy of combustion, |Δ Hc|, for the product is smaller, making (c) true.
Hydrogenation of both 1,4-pentadiene and 1,3-pentadiene yields the same alkane, pentane. Since the product (1,3-pentadiene) is more stable, it releases less heat upon hydrogenation. Therefore, the magnitude of its hydrogenation enthalpy is smaller, not greater, making (d) false.
The correct options are (a), (b), and (c).
