A single hydrogen bond between two water molecules has an energy of about

PHYSICS · Multi-part · Fermi University Physics · Biophysics & Medical Physics · Physical foundations of the living cell · Physical foundations of the living cell

Life at Thermal Energy, Ch The scales of life and the thermal energy

Problem

A single hydrogen bond between two water molecules has an energy of about 5 kJ mol−15\,\mathrm{kJ\,mol^{-1}}. A student reasons: "Once a thermal collision has supplied the 5 kJ mol−15\,\mathrm{kJ\,mol^{-1}} needed to break this bond, that energy has been spent. The bond therefore stays broken until some new external source supplies the energy again." ((a)) Convert the hydrogen bond's energy into kBTk_BT at 298 K298\,\mathrm{K}, using 1 kJ mol−1=0.404 kBT1\,\mathrm{kJ\,mol^{-1}} = 0.404\,k_BT. ((b)) Say whether this claim is correct, and justify your answer using the size of the bond energy in kBTk_BT and what the chapter says about how often hydrogen bonds in water rearrange.

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