十万个为什么·科学启蒙30篇（3）
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Why Does Hot Water Dissolve Sugar Faster?
为什么热水比冷水更容易溶解糖
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Hot water dissolves sugar faster because heat gives water molecules more kinetic energy to break apart sugar crystals.
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Sugar molecules are held together by weak attractions, and warmer water molecules collide with them more forcefully and frequently.
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Higher temperatures also increase the space between water molecules, letting more sugar particles fit between them.
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Dissolving is a physical change—not a chemical reaction—so the sugar remains chemically identical whether hot or cold.
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Stirring helps speed up dissolution in both cases by bringing fresh solvent into contact with undissolved sugar.
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However, stirring alone cannot overcome the fundamental limit set by temperature and solubility.
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At 100°C, water can hold over twice as much sugar as it can at 0°C—about 487 g per 100 mL versus 179 g.
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Once saturated, adding more sugar won’t dissolve—it’ll just settle at the bottom regardless of temperature.
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This principle applies to many solids, but gases like CO₂ actually dissolve *less* in warm water, which is why soda goes flat faster when warm.
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Understanding solubility helps cooks, pharmacists, and environmental scientists predict how substances mix in nature and industry.