Final answer:
A solution forms when substances combine physically to yield a homogeneous mixture. Whether a mixture yields a solution depends on the molecular properties of its components. Some solutions produce or absorb heat when they form due to the breaking and forming of intermolecular attractions.
Step-by-step explanation:
A solution forms when two or more substances combine physically to yield a mixture that is homogeneous at the molecular level. The solvent, which is the most concentrated component, determines the physical state of the solution. The solutes, on the other hand, are the other components present at concentrations lower than that of the solvent.
Whether a given mixture will yield a solution depends on the molecular properties of its components. Specifically, it depends on the relative magnitudes of solute and solvent intermolecular attractive forces. If the forces between the solute and solvent molecules are strong enough, a solution will form.
Some solutions either produce or absorb heat when they form because of the energy changes associated with the breaking and forming of intermolecular attractions. If the solvent-solute attractions are stronger than the solute-solute and solvent-solvent attractions, heat is usually absorbed during solution formation. On the other hand, if the solvent-solute attractions are weaker than the solute-solute and solvent-solvent attractions, heat is usually released during solution formation.