Practice Problems
1. A sample of pure ethanol (C2H6O)boils at a temperature of 78.37 degrees Celsius while a sample of H2O boils at 100 degrees Celsius at 1 atm. In terms of intermolecular forces, explain the discrepancy between the boiling points of the two substances.
2. The diatomic molecule I2 exists as a solid at STP while a similar diatomic molecule Br2 exists as a liquid in the same conditions. In terms of intermolecular forces, explain the difference in states of matter between the two substances.
3. Surfactants are substances which lower the surface tension of a liquid. For instance, soap and dish detergent are two commonly used household surfactants. A key characteristic of a surfactant is the presence of a nonpolar and polar end to a molecule of the substance. Explain in terms of intermolecular forces, why using surfactants such as soap is more effective when cleaning than simply using water is.
4. Match the following pure substances to their respective melting points under 1 atm of pressure.
2. The diatomic molecule I2 exists as a solid at STP while a similar diatomic molecule Br2 exists as a liquid in the same conditions. In terms of intermolecular forces, explain the difference in states of matter between the two substances.
3. Surfactants are substances which lower the surface tension of a liquid. For instance, soap and dish detergent are two commonly used household surfactants. A key characteristic of a surfactant is the presence of a nonpolar and polar end to a molecule of the substance. Explain in terms of intermolecular forces, why using surfactants such as soap is more effective when cleaning than simply using water is.
4. Match the following pure substances to their respective melting points under 1 atm of pressure.
H2O
CH4 C10H22 He |
-272.2 degrees Celsius
-30 degrees Celsius -182 degrees Celsius 0 degrees Celsius |