1. How many phase rule variables must be specified to fix the thermodynamic stat

Question

1. How many phase rule variables must be specified to fix the thermodynamic state of each of the following systems? Show how you determine these.
(i) A sealed flask containing liquid water in equilibrium with its vapor.
(ii) A sealed flask containing a liquid ethanol-water mixture in equilibrium with its vapor and nitrogen .
(iii) A sealed flask containing ethanol, toluene, and water as two liquid phases plus vapor.
(iv) A system of liquid n-pentane and n-heptane mixture in equilibrium with its vapor .

My second question is in this picture:
2.

Explanation / Answer

Q1.

Apply the Gibbs Phase Rule

F=C-P+2

where, F = degrees of freedom, C = compunds in system, P = Phases

so

(i) A sealed flask containing liquid water in equilibrium with its vapor.

compounds = water only, so 1

phases = vapor, liquid so 2

then

F = 1-2+2 = 1

We need to set only one variable in order to satisfy the system i.e. either T or P

(ii) A sealed flask containing a liquid ethanol-water mixture in equilibrium with its vapor and nitrogen .

C = ethanol+water+nitrogne = 3

phases = liquid+vapor = 2

F = 3-2+2 = 3

We will need to state most likely, pressure of system, liquid composition and Temperature in order to set the vapor pressure + N2gas

(iii) A sealed flask containing ethanol, toluene, and water as two liquid phases plus vapor.

C = ethanol+toluene+water = 3

P = 2 liq. phase + vapor phase = 3

F = 3-3+2 = 2, either T or P or compositions

(iv) A system of liquid n-pentane and n-heptane mixture in equilibrium with its vapor .

C = péntane + heptane = 2

P = liquid+vapor = 2

F = 2-2+2 = 2

For Q2: Please consider posting multiple questions in multiple set of Q&A. According to Chegg's Q&A Guidelines, we are only allowed to answer to one questions per Q&A.

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