• Question: Why does water a vaperate?

    Asked by anon-258676 on 14 Jul 2020.
    • Photo: anon

      anon answered on 14 Jul 2020:

      There are three principle “states” of matter – solid, liquid and gas. In simple terms they are typified by the degree of bonding between the molecules which make up the matter – H2O or two hydrogen and one oxygen atom per molecule, in the case of water. Breaking those bonds requires (vibration) energy which usually comes from heat – so adding heat to ice will melt it into water, and adding heat to water will make it evaporate into vapour (steam). Oddly, perhaps, when molecules of water part during evaporation they take heat with them – which is why sweat cools the body, as it takes that “heat of evaporation” along with it. So – water evaporates as it transforms from liquid to vapour, as bonds between molecules break apart, typically on the application of heat. Does that make sense?

    • Photo: Martin Coath

      Martin Coath answered on 15 Jul 2020:

      What Steve Thomas says is spot on. To put it another way the water molecules in liquid water are all moving around, and their speed increases with temperature.

      At *any* temperature there is always a chance that a few of them will escape the surface to become a gas (vapour) – but as the temperature is raised it is inevitable that they all will.

      Water doesn’t have an obvious smell but if you take something like peppermint oil the strong smell is the peppermint molecules escaping the liquid in the bottle at room temperature – which is why you have to keep the top closed!
      😊

    • Photo: Steve Williams

      Steve Williams answered on 15 Jul 2020: last edited 15 Jul 2020 2:24 pm

      This is an excellent question as it relates to some fundamental physics where I think Steve Thomas has given a very complete answer when referring to energy and heat and their effect on water. We tend to think of water as a liquid because that’s mostly how we encounter it because it’s in its liquid state within most of the temperature range of our climate. If we lived in a polar region we might think of water more in it’s solid state, ice. Another factor that effects the state of water is air pressure which when high will increase it’s boiling point temperature and visa versa. So when you ask a question about water and its gas state, vapour, you do open up some very interesting areas of physics. Water also has the unique property that it expands when it changes from liquid to a solid state. If water didn’t do this life on earth might not have been possible – you might like to investigate this yourself further.

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