Why is water a liquid at room temperature?

iceHbondsHydrogen Bonding – Water is a liquid at room temperature due to the presence of hydrogen bonds between water molecules.  The state of a molecule is determined by intermolecular forces, such as dipole-dipole interactions, Van der Waals forces (also called London dispersion forces), and hydrogen bonds.

Water (H2O) is unique in that it has extremely strong hydrogen bonds, but a very low molecular weight (18 grams per mole) .  Usually molecules with very low molecular weights are gases at room temperature.  Consider for example carbon dioxide (CO2) with a molar mass of 44 g/mole, which is a gas.  Other molecules with low molecular weights are nitrogen gas (N2, 28 g/mole), oxygen gas (O2, 32 g/mole), propane (C3H8, 44 g/mole) and butane (C4H10, 58 g/mole).  All of these are gases and yet have much higher molecular weights than water does.  However, none of these can hydrogen bond, and that is why they are gases, whereas water is a liquid.

Of course, at high temperatures water is a gas (steam) and at low temperatures water is a solid (ice). Via Why water is liquid at room temperature.

We guess that the pressure has an input as well – Deskarati

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2 Responses to Why is water a liquid at room temperature?

  1. Steve B says:

    Pressure is only involved where water becomes steam, and vice versa. At 1000 feet water will boil at 98.9 C, compared to 100 C at 0 feet.

    The only effect that pressure will have at room temperature would relate to the rate of evaporation of the liquid water.

  2. Phil Krause says:

    Water can only evaporate from its surface, when a molecule of water ends up going fast enough to escape the main body of water. There may be many other water molecules attain this speed but unless they are at the surface they cannot evaporate, they will just bump into other molecules. If water is heated, the temperature and therefore the average speed of the molecules will increase. Therefore more molecules with enough pace will find themselves at the surface and evaporation will become faster. However, when the vapour pressure inside the water finally equals the pressure outside the water, will the water be able to evaporate below the surface. Thats what boiling is, when the water has enough energy to evaporate throughout creating bubbles of steam which will rise to the surface because they are lighter than the surrounding water. Therefore, if you increase the outside pressure, the internal pressure within the water must increase before they become equal and the water can boil. As water is much denser than air, the pressure builds up quicker. Just 10 meters down, water won’t boil until 120 degrees C.

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