• Question: What substance can be a gas,liquid and a solid?

    Asked by to Anna, Jane, Iain, Nick on 19 Mar 2014. This question was also asked by .
    • Photo: Anna Middleton

      Anna Middleton answered on 19 Mar 2014:


      Hi cass1b0y
      I’m just thinking….can’t everything be a gas, liquid and a solid at different temperatures? I know the obvious is water/ice/steam, but I’m now thinking that if my coffee cup (a solid) was burnt it would melt (liquid) and eventually gasses would come off it (gas).

    • Photo: Iain Moal

      Iain Moal answered on 19 Mar 2014:


      There are many substances that can be a gas, liquid and a solid, and which one they are depends on their temperature and pressure. In chemistry, we show this using a phase diagram, such as the one for water here:

      On this diagram the pressure is on the left (y-axis) and the temperature is on to bottom (x-axis), and the graph shows whether the water will be liquid, gas or solid depending on these. One interesting thing about this phase diagram is that there is a point at which all three states meet, shown by the dot on the graph. What this means is that at this particular temperature and pressure, you get gas, liquid and solid existing at the same time – a layer of steam on top of a layer of ice on top of a layer of liquid water. You can even have it so that the water is boiling and freezing at the same time!

    • Photo: Jane Charlesworth

      Jane Charlesworth answered on 19 Mar 2014:


      Many things can be gases, liquid or solids–water is one of them. Whether a substance is a gas, a liquid or a solid depends on two factors: pressure and temperature. In fact, it’s even possible, if you get the right combination of pressure and temperature, for water to be a gas, a liquid and a solid all at the same time.

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