Why Does Sugar Dissolve Faster in Hot Water Than Cold?

Solvents and Solutes

In chemistry, when one substance is dissolved in another, the result is called a solution. The substance being dissolved is called the solute, and the substance it is dissolved into is called the solvent. If the solvent is water, the resulting solution is called an aqueous solution. Some solutes, like table salt (NaCl), ionize, or break up into charged particles called ions, when they go into an aqueous solution. This allows the solution to conduct electricity, which is why these substances are called electrolytes. Substances like sucrose, or table sugar (C-12 H-12 O-11), do not break up into ions and are called nonelectrolytes.

Entropy

Entropy is a measurement of randomness with respect to the motion of atoms and molecules in a sample of matter. It is also the reason substances go into solution. For example, when sugar is added to water, energy is used up to break apart the molecules in the sugar. The water molecules then begin to spread out to make room for the sugar. Both the water and the sugar experience increased entropy as this process progresses.

Temperature

According to the second law of thermodynamics, adding heat energy to a system, such as a solution, increases entropy. When heat energy is added to a sugar/water solution to increase the temperature, entropy is also increased. This means the sugar molecules beak apart faster, and the water molecules move around the sugar faster until the sugar is completely dissolved.

References

• Chemistry; Neil Jespersen, Ph.D.; 1997