When liquid water at 100 ∘C100\,^{\circ}\text{C}100∘C vaporises into steam at atmospheric pressure, its density decreases from 1000 kg m-3 to 0.60 kg m-3.
Using the simplified particle model illustrated below, where each molecule in both states is assumed to occupy a cubical region of space of volume V=d3V = d^3V=d3 (where d d\,d is the average separation between the centres of neighboring molecules), by what factor does the average molecular separation increase when water transitions from liquid to gas?
1.21.21.2
121212
414141
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