Question 6: Suppose that an iceberg (pure water in the solid form) is in the oce

Question

Question 6: Suppose that an iceberg (pure water in the solid form) is in the ocean (pure water) for a long time in
equilibrium with the surrounding air (dry-air and water vapor) at atmospheric pressure. Perform degree-of-freedom
analysis and name the intensive variables that are required to be set (if there should be any) for the system to be specified?

(hint: you may consider the air as two pseudo-components, dry air and water and assume that there are no reactions
involved).

Problem 6: Suppose that an iceberg (pure water in the solid form) is in the ocean (pure water) for a long time in equilibrium with the surrounding air (dry-air and water vapor) at atmospheric pressure. Perform degree-of-freedom analysis and name the intensive variables that are required to be set (if there should be any) for the system to be specified? (hint: you may consider the air as two pseudo-components, dry air and water and assume that there are no reactions involved)

Explanation / Answer

Here is givenn that iceberg (pure water in the solid form) is in the ocean (pure water) in equilibrium with the surrounding air (dry-air and water vapor) at atmospheric pressure.

Insted of that caonsider here a simple glass of water. the water is a single phase & decribed with various thermodynamic properties like P,T,H etc.

In our example Temperature [T] and pressure[P] are taken as independent intensive variables.Phase rule tells how many independent intensive properties F can be chosen for given system.

F= N-P+2 ...........1}

where,

number of chemical species= N, and number of phases= P

An example for a single phase of a pure substance, F=2:

A glass of liquid water, here one of independent intensive variables to be pressure. This pressure is to be 1 atm. liquid water is in the glass, the temp can take any value between 0 'C & 100 'C. Within this range, the temperature can be choosen independently of the pressure.

So, here T & P are independent. A (T, P) pair, any other property, such as volume/entropy, can be found using the steam tables/ Mollier diagram & remaining properties can't be independently choosen after T & P are specified.

An Example for two coexistant phases of a pure substance, F=1.

A glass of boiling water (saturated liquid water) in equilibrium with saturated steam, specify the one of the independent intensive variables to be pressure & this pressure is 1 atm. In order for the water to boil at this pressure, the temperature must be 100 'C. So,the temperature can't be choosen independently of the pressure when both liquid & vapor water are present. So here only P is independent.

An Example for three coexistant phases of a pure substance, F=0.

At the triple point, vapor, liquid[water] and solid [ice] coexist. For any substance, the triple point occur only at one a specific pair of temperature and pressure.It is stated the substance at the triple point, the values of this temperature & pressure pair as well as the values of all other thermodynamic property found in a table/graph. So, here no thermodynamic property can be choosen independently.

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