Sunday, April 24, 2011


There are three properties of water that make it unique.

Every single one of these properties is used in every single cuisine so it helps to understand how things work.

  • Water is a polar molecule.

    Water may be H2O but the two hydrogen atoms are attached at a 109.5° angle. This polarizes the water molecule because there is more positive charge on one side (H2+) rather than the other (O-.)

    This means water can dissolve polar molecules. Specifically, any salt.

    Most importantly, the salts will be split into their ionized components when dissolved because the positive ions will be attracted to the negative portion of the water molecule (O-) and the negative ions to the positive portion (H2+.)

  • Water has a very high boiling point.

    Water is a very small molecule. However, compared to molecules of its size, it has an absurdly high boiling point. This is due to its polar nature. Water molecules naturally attract each other and it's quite hard to separate them. That's also why the phase transitions (ice → water, water → steam) take so much heat.

  • Water has a very high specific heat.

    This just means that water can hold a tremendous amount of heat i.e. it has a high thermal capacity.

    Heat is just the average energy of motion of a molecule.

    This is a tricky point so it requires some explanation.

    Whenever a molecule is symmetric, its bonds restrict a certain degree of vibration along the bonds because too much movement would break the bonds.

    So a linear molecule is restricted in its motion along the line. If you had a molecule symmetric in two directions, its motion would be restricted in the plane but it could still rotate along both axes.

    Water is so asymmetric that all three rotational degrees of freedom are possible as well as vibrating along both bonds, and perpendicular to them, and none of them break up the molecule so it can absorb energy to "spin" in three directions, and "vibrate" in three as well. Hence, it can absorb a lot of energy to "move".

    Most importantly, it's the smallest molecule that has this property.
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