(a) A liquid and a gas are moved to larger containers. How does their behavior differ once they are in the larger containers? Explain the difference in molecular terms. (b) Although liquid water and carbon tetrachloride, \(\mathrm{CCl}_{4}(l),\) do not mix, their vapors form a homogeneous mixture. Explain. (c) Gas densities are generally reported in grams per liter, whereas liquid densities are reported in grams per milliliter. Explain the molecular basis for this difference.

When a liquid and a gas are moved to larger containers, their behavior differs due to differing intermolecular forces and the amount of free space available between the molecules. For a liquid, the intermolecular forces are stronger, which maintains the liquid's constant volume. When placed in a larger container, the liquid will simply occupy the same volume as before, but in the larger container, it will seem to take up less space as it does not expand to fill the entire container. On the other hand, a gas has weak intermolecular forces, and the molecules are in constant motion. When placed in a larger container, the gas will expand to fill the entire available space due to the high kinetic energy of its molecules. Consequently, the gas becomes more spread out, decreasing its overall pressure.

Liquid water and carbon tetrachloride do not mix because they have different types of molecules. Water is a polar molecule due to the electronegativity difference between oxygen and hydrogen atoms, while carbon tetrachloride has a nonpolar molecule with evenly distributed electron density. Since "like dissolves like," polar and nonpolar molecules don't tend to mix well because polar molecules prefer to interact with other polar molecules and nonpolar molecules prefer to interact with other nonpolar molecules. Their vapors, however, can form a homogeneous mixture because they are both in the gas phase. In the gas phase, the intermolecular forces that would prevent polar and nonpolar liquids from mixing become less significant due to the high kinetic energy of the molecules. As a result, the different types of molecules can mix freely, forming a homogeneous gaseous mixture.

The molecular basis for using different density units for gases (grams per liter) and liquids (grams per milliliter) is due to the difference in the packing of molecules and the magnitude of their intermolecular forces. In a liquid, the molecules are more closely packed together, and the intermolecular forces are stronger compared to a gas. As a result, the mass of the molecules present in a given volume is considerably higher in liquids than in gases. Therefore, expressing liquid densities in grams per milliliter (a smaller unit of volume) is more appropriate as it provides a more manageable number and better representation of this higher mass concentration. In contrast, gas molecules have much weaker intermolecular forces and are far more spread out. This results in a much lower concentration of mass per given volume. To accurately represent this less concentrated mass, gas densities are reported in grams per liter (a larger unit of volume), which is a more suitable and convenient unit for gases.