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50 g benzaldehyde vapour is condensed at 179°C, What is the enthalpy of the liquid relative to the vapour? Given: The molecular weight of benzaldehyde is 106.12, the normal boiling point is 179.0°C and the standard heat of vaporization is 38.40 kJ gmol-1. For condensation the latent heat is – 38.40 kJ gmol-1.

50 g benzaldehyde vapour is condensed at 179°C, What is the enthalpy of the liquid relative to the vapour? Given: The molecular weight of benzaldehyde is 106.12, the normal boiling point is 179.0°C and the standard heat of vaporization is 38.40 kJ gmol-1. For condensation the latent heat is – 38.40 kJ gmol-1. Correct Answer -18.09 kJ

ΔH = 50 g (- 38.40 kJ gmol-1). |(1 gmol)/(106.12 g)| = -18.09 kJ Therefore, the enthalpy of 50 g benzaldehyde liquid relative to the vapour at 179°C is – 18.09 kJ. As heat is released during condensation, the enthalpy of the liquid is lower than the vapour.

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