Why is hot water a better solvent than cold water? © Acute Graphics

Why is hot water a better solvent than cold water?

Energy from hot water molecules makes solids more soluble.

Asked by: Michelle du Bois, Portland, Oregon, USA

Advertisement

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

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.

Is water always necessary for life? © iStock

Advertisement

Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun facts.