Question

The difference between heat of reaction at constant pressure and constant volume for the reac
given below at 25°C in kJ is:
Alg) +3BG) ► 0(g)​

Answer 1

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 + (Δn

g

)RT

where, Δn

g

= change in number of gaseous moles in any reaction.

Since, in the above reaction the only gaseous species are CO

2

and O

2

, so,

Δn

g

=12−15=−3.

Hence, using ΔH - ΔU = (Δn

g

)RT

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

=> ΔH - ΔU=7430J=7.43KJ

Hence, answer is option C.

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