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Using the heats of fusion and vaporization for water given in Exercise 101 calculate the change in enthalpy for the sublimation of water:

H₂O(a) → H₂O(g)
Using the ∆H value given in Exercise 116 and the number of hydrogen bonds formed with each water molecule, estimate what portion of the intermolecular forces in ice can be accounted for by hydrogen bonding.

User Littlemad
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Final answer:

The enthalpy of sublimation for water can be calculated by adding the enthalpy of fusion (6.0 kJ/mol) and the enthalpy of vaporization (40.7 kJ/mol). Hydrogen bonding significantly contributes to intermolecular forces in ice, with each molecule forming four hydrogen bonds.

Step-by-step explanation:

To calculate the change in enthalpy for the sublimation of water, you can use the enthalpy of fusion and the enthalpy of vaporization, assuming that sublimation is a two-step process where ice first melts into water (fusion) and then water vaporizes into steam (vaporization). According to the information provided, ice has an enthalpy of fusion of 6.0 kJ/mol at 0°C. Once the ice turns into liquid water, the water then vaporizes, which requires an enthalpy of vaporization of 40.7 kJ/mol at 100°C. So, the enthalpy of sublimation of ice can be estimated by adding the enthalpy of fusion and the enthalpy of vaporization.

The number of hydrogen bonds formed with each water molecule in ice can also be considered when looking at the portion of intermolecular forces accounted for by hydrogen bonding. Each water molecule can form four hydrogen bonds, which contribute significantly to the stability of the ice structure. The substantial amount of energy required for phase changes is partly the result of needing to overcome these hydrogen bonds, which implies that hydrogen bonding accounts for a significant portion of the intermolecular forces in ice.

User Venky Viswanath
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