Answer:
The intermolecular forces between the solute and solvent.
Explanation:
When you are heating a solvent, the intermolecular forces are reduced because the distances between molecules are large. Thus, in a solution where solvent is hot the intermolecular forces between solute and solvent are lower than those solutions where solvent is in room temperature.
The covalent bonds do not change because this mean a chemical reaction that doesn't occur in a solution.
Usually solid solutes melts in a higher temperature than boiling point in solvents. Thus, a compound normally doesn't melt in a hot solvent.
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