Physical Properties of Substances Flashcards
Between ionic and covalent compounds, which have a higher melting/boiling point and why?
Ionic compounds have higher melting or boiling points because they are composed of positively and negatively charged ions held together by strong electrostatic forces which require a lot of energy to break. In contrast, covalent compounds have molecules held together by intermolecular forces, which are generally weaker than ionic bonds.
Everyone knows that oils and fats do not dissolve well in water. How can you explain that in terms of molecular structure?
think if oils and fats are polar or nonpolar!
The molecular structure affects solubility based on polarity. Oils and fats are nonpolar substances and therefore tend to dissolve in nonpolar solvents.
Polar substances (like water) dissolve other polar substances (like salt) due to the attraction between positive and negative charges. Nonpolar substances, like oil and fats, dissolve better in nonpolar solvents like hexane.
Explain why, in addition to polarity, the size of a molecule also influences its boiling/melting point.
This is due to London dispersion forces. Larger molecules have more electrons and greater surface areas, leading to stronger dispersion forces. This results in higher boiling and melting points compared to smaller molecules with weaker dispersion forces.
A substance with a** low boiling point** will have a relatively (lower/higher) equilibrium vapor pressure.
Higher. When a substance has a low boiling point, it means it reaches its equilibrium vapor pressure more quickly, hence a higher vapor pressure at a given temperature.
In other words, substances with low intermolecular forces (and low boili
Which compound has a lower vapor pressure at equilibrium, salt or water?
Water (H2O).
Water is a covalent compound, its molecules are held together by hydrogen bonds, which are weaker than the ionic bonds in NaCl. Consequently, water has a much lower melting point and a higher equilibrium vapor pressure compared to NaCl, making it much more volatile.
