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Stoichiometry - Engineering

Q1:

The heats of vaporisation of CS2, C2H5OH &H2O are 26.8, 38.6 & 40.6 KJ/kg mole respectively. The order of decreasing inter-molecular forces in these liquids is

A H2O > C2H5OH > CS2

B CS2 > C2H5OH > H2O

C H2O > CS2 > C2H5OH

D CS2 > H2O > C2H5OH

ANS:A - H2O > C2H5OH > CS2

The heat of vaporization is a measure of the energy required to change a substance from a liquid to a gas at its boiling point. Higher heat of vaporization generally indicates stronger intermolecular forces, as more energy is needed to break these forces and convert the substance into a gas. Given the heats of vaporization provided:

  • CS2: 26.8 kJ/kg mole
  • C2H5OH (ethanol): 38.6 kJ/kg mole
  • H2O (water): 40.6 kJ/kg mole
We can infer that the substance with the highest heat of vaporization (H2O) has the strongest intermolecular forces, followed by C2H5OH (ethanol), and finally CS2. So, the correct order of decreasing intermolecular forces in these liquids is: 𝐻2𝑂>𝐢2𝐻5𝑂𝐻>𝐢𝑆2H2​O>C2​H5​OH>CS2​