Which member of each of these pairs of substances would you expect to have a hig
ID: 532496 • Letter: W
Question
Which member of each of these pairs of substances would you expect to have a higher boiling point: (a)O_2 or N_2: (b) SO_2 or CO_2, (c) HF or HI? (d) pentane or 2-methyl-butane? e) CH_3 CH_2 OH or CH_3 OCH)3? State which substance in each of these pairs you would expect to have the higher boiling point and explain why: (a) Ne or Xe, (b) CO_2 > or CS_2, (c) CH_4 or Cl_2, (d) F_2 or LiF, (e) NH_3 or PH_3. Define surface tension. What is the relationship between the intermolecular forces that exist in a liquid and its surface tension? Use water and mercury as examples to explain adhesion and cohesion. Consider the following: Ethylene glycol (this goes in your car - do you know what for?) Ethanol (the principal type of alcohol that you find in alcoholic beverages) Glycerol (If you are a biology major, you should know what this is.) After looking at these three molecules, which one do you think has the greatest viscosity? Why? Define boiling point. How does the boiling point of a liquid depend on external pressure?Explanation / Answer
1. a. O2
b. SO2
c. HI
d. Pentane
e. CH3CH2OH
2. a. Xenon has a higher boiling point than neon because it exhibits stronger intermolecular forces.
b. CS2 has a higher boiling point than CO2 despite having similar intermolecular forces because it has a larger molar mass.
c. Chlorine is a heavier molecule and is diatomic. This is why chlorine has a higher boiling point.
d. F2
e. The boiling point of NH3 is higher than that of PH3 due to the hydrogen bonding in the former.
3. Surface Tension:- The tension of the surface film of a liquid caused by the attraction of the particles in the surface layer by the bulk of the liquid, which tends to minimize surface area.
The stronger the intermolecular forces that are holding a liquid together, the more energy that will be required to pull them apart. What this means in practicle terms is that a liquid with strong intermolecular forces will have to be heated to a higher temperature before it will evaporate.
4. The force of attraction between molecules of the same substance is called Cohesion, as distinct from Adhesion or the force between molecules of different substances.
The adhesion of water to glass is stronger than the cohesion of water. Hence, when water is spilled on a clean glass surface it wets the glass and spreads out in a thin film. On the other hand, the cohesion of mercury is greater than its adhesion to glass. Therefore, when mercury is spilled on glass it forms small spherical droplets or larger flattened drops.
The difference between the adhesive and cohesive properties of water and mercury explains why meniscus of water curves upwards and that of mercury curves downwards when these liquids are poured into clean glass vessels
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