Engineering Chemistry MCQ (Gibb’s Phase Rule)
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Gibb’s Phase Rule
1. What does Gibb’s phase rule state?
Explanation: The above phase rule is a formula that gives the condition for finding
the number of phases in a system. This phase rule can be applied to both condensed as well as normal systems.
2. What is the point at which all the three phases of a system exist?
a) Triple point
b) Sublimation point
c) Vapor point
d) Eutectic point
Explanation: Since at the triple point, the degree of freedom is zero (that is invariant
reaction takes place at that point), therefore according to phase rule, F=C-P+2. Substituting the known values, we get P=3 (all states).
3. For water system, the number of phases at the triple point is _____________
Explanation: Since at the triple point, the degree of freedom is zero, while applying
the formula F=C-P+2, we get the number of phases as three because C=1, F=0 (since water system forms only single component).
4. Liquid phase exists for all compositions above _________ region.
a) Eutectic region
b) Equilibrium region
c) Isometric region
d) Sublimation region
Explanation: In a phase region above the eutectic point, both the solid and liquid
phases exist together where the region is bi variant and this region is called
isometric region. Here the region has 2 degrees of freedom.
5. Select the wrong statements from the following statements with respect to a phase diagram.
a) Gives information about concentration
b) Gives information about solubility
c) Gives information on melting and boiling points
d) Gives information on relative concentration
Explanation: A phase diagram gives information only on the concentration of
species, their solubility rate, degree of freedom and other physical properties. It
does not explain about transformation rates and relative concentration (relative concentration=total concentration/equilibrium concentration).
6. Select a non-homogeneous system from the following.
a) Salt solution
b) Sugar solution
c) Glucose in water
d) Saturated solution of NaCl
Explanation: A homogeneous mixture is one which is miscible completely with one
another. In any saturated solution, when the amount of solute reaches more than a critical point, then the solution becomes heterogeneous.
7. Select the odd statement with respect to a phase reaction.
a) Saturated solution
b) Equilibrium solution
c) Concentric solution
d) Amorphous solution
Explanation: A terminal solution, an intermediate solution, an equilibrium solution
and concentric solutions, are the ones which take part in a phase reaction. On the
other hand, a saturated solution is involved in the Lever system.
8. Which of the following is the formula for condense phase rule?
Explanation: In a condensed phase rule system, the phases are represented in three
dimension which is not suitable for graphic purposes and hence the pressure is
considered to be zero (this is helpful in drawing 2D images). Hence the formula reduces to F=C-P+2.
9. Calculate the eutectic concentration given the following data. Pressure= 1atm Temperature: 1oC
Explanation: According to Weiss law (which suits only for phase components),
concentration at equilibrium is C=T/P. therefore in this case, C=1/1=1. This law is
also called as Gibbs relativity law.
10. Under what condition, will we get a stable phase diagram?
a) Solid + Liquid
b) Solid + Vapor
c) Liquid + vapor
d) Liquid + Solid
Explanation: According to equilibrium mixture ration, an appropriate ratio of 1:10
parts of solid and liquid along with an aqueous solution will give a stable phase