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Water is strange. This practice quiz will examine the molar heat capacities for

ID: 1320881 • Letter: W

Question

Water is strange. This practice quiz will examine the molar heat capacities for liquid water and solid water. One mole (of water molecules) in the liquid phase has a heat capacity of c = 75.2 J/K One mole of water molecules in the solid phase (ice, ice baby) has molar specific heat of c = 36.9 J/mol*K a) For liquid water, how many modes per molecule of water are active? How many modes per atom? b) For solid water, answer the same question. How many modes are active per molecule? How about per atom? Moral of the story: 1) We don't always have the same number of modes per molecule in the solid and liquid phase, let alone the gas phase! 2) Sometimes, even in a solid or liquid modes can be frozen out!

Explanation / Answer

Degree of Freedom or modes per molecule = C/(R/2), where C = molar heat capacity & R = gas constant

a) For liquid water,

Modes = 18 per molecule = 6 per atom

b) For solid water

Modes = 9 per molecule = 3 per atom