Gases and STP
What is the value of standard temperature in degrees Celsius?
0°C.
What type of intermolecular force is present between nonpolar molecules?
London dispersion forces (or van der Waals forces).
Which property of a liquid increases with stronger intermolecular forces: boiling point or volatility?
Boiling Point
Between CH4 and NH3, which molecule has stronger intermolecular forces?
NH3, because it has hydrogen bonding.
Why does water form droplets on a waxy surface instead of spreading out?
Due to strong cohesion (hydrogen bonding) within water and weak adhesion with the wax.
What is the value of standard pressure in kilopascals (kPa)?
101.3 kPa.
What is the strongest type of intermolecular force present in water?
Hydrogen Bonding
True or False: Substances with weak intermolecular forces tend to have lower melting points.
True
Which would have a higher boiling point, HCl or Cl2?
HCl, because it has dipole-dipole interactions, while Cl2 only has London dispersion forces.
Why do perfumes evaporate quickly when applied to the skin?
Perfumes contain volatile substances with weak intermolecular forces, allowing them to evaporate easily.
At STP, 1 mole of any ideal gas occupies what volume?
22.4 litres.
Which intermolecular force is present between polar molecules but not involving hydrogen?
Dipole-dipole interactions.
What happens to the viscosity of a liquid as the strength of intermolecular forces increases?
Viscosity increases.
Why does HF have a higher boiling point than HCl, even though both are polar molecules?
HF has hydrogen bonding, which is stronger than the dipole-dipole interactions in HCl.
What type of intermolecular forces must be overcome when boiling ethanol?
Hydrogen bonding and dipole-dipole interactions.
Calculate the number of moles of gas in 44.8 L at STP.
2 moles.
Rank these intermolecular forces from weakest to strongest: London dispersion, dipole-dipole, hydrogen bonding.
London dispersion, dipole-dipole, hydrogen bonding.
Which type of intermolecular force would you expect to be dominant in a molecule like HCl?
Dipole-dipole interactions.
Arrange the following in order of increasing boiling point: CH4, C2H6, C3H8.
CH4, C2H6, C3H8 (boiling point increases with increasing molecular size and stronger London dispersion forces).
How do intermolecular forces explain why oil and water do not mix?
Water has strong hydrogen bonds, while oil has only London dispersion forces. The difference in intermolecular forces prevents them from mixing.
A sample of gas occupies 11.2 L at STP. How many molecules are in the sample?
6.02×1023 molecules (1 mole).
Which intermolecular force is responsible for the unusually high boiling point of water?
Hydrogen bonding.
Explain why ionic compounds generally have higher melting points than molecular compounds.
Ionic compounds have strong electrostatic forces of attraction between ions, which require more energy to overcome compared to the intermolecular forces in molecular compounds.
Between CO2 and SO2, which would have stronger intermolecular forces and why?
SO2, because it is polar and exhibits dipole-dipole interactions, whereas CO2 is nonpolar and only has London dispersion forces.
Why is ice less dense than liquid water?
In ice, water molecules are arranged in a lattice structure due to hydrogen bonding, which takes up more space and makes ice less dense than liquid water.