Question

What is the difference between heats of reaction in lit-atm at constant pressure and constant volume
when 0.1 mole of C7H8 undergoes the given reaction at 500 K?
C7H8(l) + 9O2(g) -> 7CO2(g) +4H2O(l)​

Answer 1

Answer:

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

Explanation:

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