• Question: If salt is added to water will the solution make the salt dissolve at the same temperature as the water?

    Asked by Resh@science to Hayley, Jimi on 17 Mar 2016.
    • Photo: Hayley Moulding

      Hayley Moulding answered on 17 Mar 2016:

      The water will heat up a little bit to be able to dissolve the salt. But a really really small amount. Sometimes though, the water might cool slightly. A really small amount. It is because when salt is dissolved it can either give out heat, or make the surrounding cooler.

    • Photo: Jimi Wills

      Jimi Wills answered on 17 Mar 2016:

      it depends on the type of salt… and how much salt is already on the solution.

      it also depends on what type of salt you’re talking about.

      Common salt, sodium chloride (NaCl) has a heat of solution +4 KJ/mol. That means that you need to give it energy to dissolve it. And that energy comes from the heat in the water… so the water cools down. The specific heat capacity of water is about 4 KJ per litre per degree. So if you tried to dissolve 1 mol of NaCl (about 60 grams) in 1 litre of water, the water would get 1 degree colder.

      Ammonium bicarbonate, another salt that is used in baking and in the lab, has a heat of solution of about -32 KJ/mol, so if you dissolved 1 mol (about 80 grams) in 1 litre of water, the water would get 8 degrees hotter.

      BUT

      you’ll learn all about this at secondary school 🙂

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