A closed system containing water, methanol, and ethanol is found to contain vaporand liquid at equilibrium. How many intensive variables is it possible to vary withoutchanging the number of phases in coexistence?a. 0b. 1c. 2d. 3
Question
A closed system containing water, methanol, and ethanol is found to contain vaporand liquid at equilibrium. How many intensive variables is it possible to vary withoutchanging the number of phases in coexistence?a. 0b. 1c. 2d. 3
Solution
The answer is c. 2.
This is based on the phase rule in thermodynamics, which states that F = C - P + 2, where F is the number of degrees of freedom (intensive variables that can be varied independently), C is the number of components, and P is the number of phases.
In this case, we have three components (water, methanol, and ethanol) and two phases (vapor and liquid). So, F = 3 - 2 + 2 = 3.
However, since the system is at equilibrium, the temperature and pressure are not independent (they are related by the vapor pressure of the substances). So, we have to subtract one from the number of degrees of freedom, leaving us with 2 intensive variables that can be varied independently.
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