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X(g)+4Y(g)→2Z(g), ΔH∘=−75.0 kJ Before the reaction, the volume of the gaseous mixture was 5.00 L. After the reaction, the volume was 2.00 L. Calculate the value of the total energy change, ΔE, in kilojoules.

Verified Answer :


Isobaric transition, first law: H=ΔU+w

for a gas expansion: w=Pext∗ΔV

to convert to joules, you need the gas constants.

R = 0.08206 L atm/molK, R=8.314 J/molK

w=Pext∗ΔV∗8.314 J/mol∗K0.08206 L atm/mol∗K

ΔU=ΔH−[Pext∗ΔV∗8.314 J/mol∗K0.08206 L atm/mol∗K]

ΔU=−75000 J−[(43.0atm)∗(2−5)L∗8.314 J0.08206 L atm]

Then you need to convert to kJ.
by the way U=E, internal energy.