Engineering Chemistry MCQ (Application of Phase Rule)
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Application of Phase Rule to One Component System
1. Which of the following equilibriums can phase rule be applies to?
c) Isometric and Isobaric
Explanation: Since phase rule can be applied to factors like solubility, concentration,
reversibility of reaction, temperature, pressure, molecular weight, atomic weight,
strength of molecules etc (since these parameters are applicable for isometric and
isobaric states), phase rule can be applied to both isometric and isobaric equilibriums.
2. What kind of particles can phase rule be applied to?
d) Heavy particles
Explanation: Since the factors like solubility, concentration, reversibility of reaction,
temperature, pressure, molecular weight, atomic weight, strength of molecules etc
becomes negligible for microscopic particles, phase rule identifies only heavy particles.
3. What kind of behavior can phase rule identify?
a) Molecular behavior
b) Linear behavior
c) Curvic behavior
d) Atomic behavior
Explanation: In a general phase relation between temperature and concentration of
the component of various systems, the general graph will show a proportionate
relation between the two factors and hence phase rule identifies linear behavior.
4. For Gibbs free energy along a system path for a transformation from state 1 to state 2, the reaction kinetics can be expressed by __________
a) Rate = C exp(-ΔG1/RT)
b) Rate = C exp(-ΔG2/RT)
c) Rate = G/RT
d) Rate = RT/G
Explanation: In the above problem, we can see that the reactions coordinate
increases as the energy increases up to certain point above equilibrium and then it
gradually decreases. This system represents a system at stable point of time. Thus
according to energy phase relation, the rate of reaction is Rate = C exp(-ΔG1/RT).
5. According to Gibbs phase rule for a 2-component system under condensed rule, what observation can be made within the equilibrium phase?
a) T can be varied independently
b) Varying a T value fixes the equilibrium compositions
c) Neither T nor concentration can be varied respectively
d) 2 phases cannot coexist
Explanation: During invariant position of the system (equilibrium state), sometimes
due to increase in colligative properties of materials, the equilibrium faces a shift
slightly. In this case, the equilibrium can be brought back by varying T values.
6. If the following conditions result in the formation of a regular solution?
a) Ω = 0
b) Ω > 0
c) Ω < 0
d) Ω = 10
Explanation: We know that as the resistance increases, conductance decreases. This
happens at higher temperature and pressure. Thus a regular solution will be
formed only when conductivity of the solution is high. Thus the required condition is Ω < 0.
7. With respect to the general phase diagram of two component system. Identify the type of solution formed at the eutectic point.
a) Regular solution
b) Steady state solution
c) Invariant solution
d) Transition solution
Explanation: From the general phase diagram, the concentration of the first
component with respect to the other decreases till certain point (eutectic point) and
then increases gradually such that the other component’s concentration increases
together. Thus this is an example of regularity and hence a regular solution is obtained.
8. With respect to the phase diagram of copper zinc system. There happens a phase transition at a particular point. There happens an equilibrium shift consequently. At which point will zinc reach its maximum concentration?
a) Some point between transition and shift
b) After transition
c) Before shift
d) At the end of both transition and shift
Explanation: We know that all the transitions (equilibrium and phase transitions)
take place within the range 200 to 400 which is the normal equilibrium range.
According to Gibbs phase rule, zinc will reach its maximum concentration after
equilibrium point that is at the eutectic point.
9. In the general phase diagram of water component system, the region that separates solid and liquid is called _______________
a) Fusion curve
b) Sublimation curve
c) Metastable curve
d) Critical curve
Explanation: In a water component system, sometimes the water may not undergo
transition between solid to liquid instead directly gets converted from solid to
vapor. This is a stable state where a small variation in composition or temperature
may destroy the steadiness. This point is called sublimated curve.
10. During an experiment, a slight variation causes deposition of the component in its solid state. From the given data, calculate the amount of component deposited.
Temperature at equilibrium=0
Atmospheric temperature=217.7 k
Explanation: We know that according to Weiss law, concentration=
temperature/pressure (this law suits only for phase components). In this problem,
since the temperature corresponding to the deposition point is 0. Therefore, the
concentration is zero which means that ideally, no deposition has taken place.