10.5 Water


Summary

Water, with its bent structure and electronegative oxygen atom, forms hydrogen bonds due to negative and positive poles. Solid water molecules arrange in hexagonal structures with gaps, causing ice to float due to lower density than liquid water. Water's high molar enthalpy of fusion and vaporization, along with its specific heat capacity, reflect the energy needed to break strong intermolecular bonds and transition between states. Calculating energy for fusion involves multiplying the molar enthalpy of fusion by the number of moles of water, like in the example where 15.7 kJ are released when 47 grams of water freeze.


Structure of Water

Water has a bent structure with an oxygen atom that is more electronegative, leading to negative and positive poles which allow the formation of hydrogen bonds. In solid form, water molecules are linked in hexagonal structures with empty space, causing ice to float.

Density of Water

Water has a density of one gram per cubic centimeter, while ice has a density of about 0.92 grams per cubic centimeter. The molar enthalpy of fusion of water is 40.79 kJ/mol, requiring energy to break the strong intermolecular forces.

Enthalpy of Vaporization

The enthalpy of vaporization of water is 40.79 kJ/mol, which is significant due to the strong hydrogen bonds that need to be overcome to vaporize water. Water's specific heat capacity also plays a role in its low vaporization rate.

Energy Calculation for Fusion

To calculate the energy required for fusion, multiply the molar enthalpy of fusion of water (18.02 kJ/mol) by the number of moles of water. For example, 15.7 kJ of energy are released when 47 grams of water freeze.

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