4. For each pair, indicate which molecule will have a higher vapor pressure. Explain (1 Mark):
a. KCl and HCl b. HCl and NH3 c. CH3Cl and CaCl2 d. H2Te and H2
Answers
Answer:
The answer is:
a) HCl
b) HCl
c) CH₃Cl
d) H₂
Explanation:
The vapor pressure is inversely proportional to the strength of the intermolecular forces present.
Stronger the inter molecular forces, lesser the tendency to escape the liquid surface and thus lesser the vapor pressure of a liquid.
Generally,
Ionic forces are stronger than dipole interactions.
hydrogen bonds are stronger than dipole interactions
ionic or dipole forces are stronger than london dispersion forces.
Let us check the kind of intermolecular forces present:
a. KCl and HCl: Kcl is an ionic compound so will have more stronger Inter molecular forces than HCl, hence HCl will have higher vapor pressure.
b. HCl and NH₃ : NH₃ has strong hydrogen bonds present so it will have lower vapor pressure than HCl.
c. CH₃Cl and CaCl₂: Calcium chloride is an ionic compound so will have stronger inter molecular forces than chloromethan, thus CH₃Cl will have higher vapor pressure.
d. H₂Te and H₂ : Hydrogen is a small molecule so will have less dispersion forces than H₂Te, thus hydrogen will have higher vapor pressure.