Question

calculate the difference in heat of reaction at constant pressure and volume for the reaction
2C6H6(l) + 15O2---------->12CO2(g) + 6H20(l)​

Answer 1

Explanation:

The heat of reaction is basically ΔH at constant pressure and is ΔU at constant volume.

Since, for any reaction the relation between this heats is given by equation,

ΔH = ΔU + (Δng)RT

where, Δng = change in number of gaseous moles in any reaction.

Since, in the above reaction the only gaseous species are CO2 and O2, so,

 Δng=12−15=−3.

Hence, using ΔH - ΔU = (Δng)RT

 ΔH - ΔU =(−3)RT=(−3)×8.314×298.15J      (T in Kelvin)

=>  ΔH - ΔU=7430J=7.43KJ