Which member in each pair of liquids has the lower vapour pressure at a given temperature? Explain.

(a) HOCH2CH2OHorCH3CH2CH2OH

(b) CH3COOHorCH32C=O

(c) HF or HCl

Short Answer

Expert verified
  1. HOCH2CH2OHorCH3CH2CH2OH : HOCH2CH2OHvapour pressure is lower than the CH3CH2CH2OH.
  2. CH3COOHor CH32C=O:CH3COOH vapour pressure is lower than the CH32C=O.
  3. HF or HCl: HF vapour pressure is lower than the HCl.

Step by step solution

01

Intermolecular Forces 

Intermolecular forces are the interaction which are formed by the attraction of the two having opposite charges (partial positive and partial negative charge). The opposite charge are formed by the presence of the electron-negative atom in the molecule. Due to the presence of an electron-negative atom, there is and induced partial positive charge is generated on the electron-positive charge (or less electron-negative charge) atom. There will be an attraction between the both oppositely charges to form a bond.

Vapour pressure may be defined as the pressure exerted by the vapour over a certain area. The vapour pressure is inversely proportional to the intermolecular forces.

02

Vapour Pressure Explanation

(a)HOCH2CH2OHor CH3CH2CH2OH:Hydrogen bond is the bond between the electronegative atom and electropositive atom. The molecule CH3CH2CH2OHshows hydrogen bonding between electronegative O-atom and electropositive H-atom whereas in the HOCH2CH2OHmolecule there is hydrogen bonding from both sides of the molecule. As the hydrogen bonding is greater than in HOCH2CH2OH, due to the more force of attraction the vapour pressure is lower.

(b)CH3COOHor CH32C=O:Hydrogen bond is the bond between the electronegative atom and electropositive atom. The molecule CH32C=Oshows hydrogen bonding between electronegative O-atom and electropositive H-atom whereas in the CH3COOHmolecule there is hydrogen bonding from both sides of the molecule. As the hydrogen bonding is greater than in , CH3COOHdue to the more force of attraction the vapour pressure is lower.


(c) HForHCl: The hydrogen bond is the bond between the electronegative atom and the electropositive atom. The molecule HCl shows hydrogen bonding between electronegative O-atom and electropositive H-atom whereas in the HF molecule there is hydrogen bonding from both sides of the molecule. As the hydrogen bonding is greater than in HF, due to the more force of attraction the vapour pressure is lower.

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