What factor primarily affects the solubility of a substance in a solvent?

The primary factor affecting the solubility of a substance in a solvent is temperature. As temperature increases, the kinetic energy of molecules increases, leading to more frequent and effective collisions between solute and solvent molecules. This often results in enhanced solubility, especially for solid solutes in liquid solvents. For most solids, higher temperatures allow more solute to dissolve, demonstrating the direct relationship between temperature and solubility.

In contrast, while pressure can significantly influence gas solubility (as described by Henry's law), it has a minimal effect on the solubility of solids and liquids in most cases. The pH of the solvent can affect the solubility of certain compounds, particularly those that can ionize or participate in acid-base reactions, but it does not have as universal an impact as temperature does. Lastly, the concentration of other solutes primarily affects the overall solution properties, such as colligative properties or the common ion effect, rather than acting as a direct modifier of a solute's inherent solubility in the solvent.