Why is hot water a bet­ter sol­vent than cold water?

Focus-Science and Technology - - Q&A - MICHELLE DU BOIS, PORT­LAND, ORE­GON, USA

A sol­vent is a sub­stance that can dis­solve other sub­stances – water is a good sol­vent. Dis­solv­ing a solid re­quires en­ergy in­put to dis­rupt the forces hold­ing the mol­e­cules to­gether, both in the solid and the water. Most solids, in­clud­ing sugar and salt, be­come more sol­u­ble with in­creas­ing tem­per­a­ture. This is be­cause heat in­creases molec­u­lar move­ment, caus­ing more col­li­sions be­tween the water mol­e­cules and the solid. But the op­po­site is true for gases, which tend to be­come less sol­u­ble as a sol­vent’s tem­per­a­ture in­creases. As the gas mol­e­cules be­come more ac­tive, they can break free from the liq­uid, which ex­plains why drinks soon lose their car­bon diox­ide fizz on a hot day.

In hot water, mol­e­cules are mov­ing around more, so there are more col­li­sions be­tween the water mol­e­cules and a solid

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