Phase Equilibrium MCQ Quiz - Objective Question with Answer for Phase Equilibrium - Download Free PDF
Last updated on Jul 15, 2025
Latest Phase Equilibrium MCQ Objective Questions
Phase Equilibrium Question 1:
The phase diagram of a single component system is given below.
The option with the correct number of degrees of freedom corresponding to the labelled points i, j, and k, respectively, is
Answer (Detailed Solution Below)
Phase Equilibrium Question 1 Detailed Solution
CONCEPT:
Degrees of Freedom in Phase Diagrams
F = C - P + 2
- The degrees of freedom (F) of a system can be calculated using the Gibbs phase rule:
- C is the number of components in the system (in this case, a single component system, so C = 1),
- P is the number of phases in equilibrium at the point in the phase diagram.
- At different points in a phase diagram, the number of phases (P) can vary, affecting the degrees of freedom.
EXPLANATION:
- For example:
- At point j, three phases meet (P = 3), so the system has zero degrees of freedom (F = 0).
- At point i, two phases meet (P = 2), so the system has one degree of freedom (F = 1).
- At point k, the system is in a single phase (P = 1), so the system has two degrees of freedom (F = 2).
- At point i (boundary between two phases), there is 1 degree of freedom because temperature and pressure can be varied independently.
- At point j (triple point where three phases meet), there are zero degrees of freedom because all variables (temperature and pressure) are fixed by the equilibrium of the three phases.
- At point k (single phase region), there are 2 degrees of freedom because both temperature and pressure can be varied independently.
Therefore, the degrees of freedom corresponding to points i, j, and k are 0, 1, and 2, respectively.
Phase Equilibrium Question 2:
The expressions for the vapour pressure of solid (𝑝1) and vapour pressure of liquid (𝑝2) phases of a pure substance, respectively, are
The triple point temperature of this substance is ____ K (in integer).
Answer (Detailed Solution Below) 400
Phase Equilibrium Question 2 Detailed Solution
CONCEPT:
Triple Point Temperature and Vapor Pressure Equality
ln(p1) = ln(p2)
- The triple point of a substance is the unique temperature and pressure at which all three phases (solid, liquid, and gas) coexist in equilibrium.
- At the triple point, the vapor pressure of the solid phase (p1) is equal to that of the liquid phase (p2):
- Given expressions:
- ln(p1) = -2000/T + 5
- ln(p2) = -4000/T + 10
EXPLANATION:
- At the triple point:
ln(p1) = ln(p2)
⇒ -2000/T + 5 = -4000/T + 10 - Rearranging terms:
-2000/T + 4000/T = 10 - 5
⇒ 2000/T = 5 - Solving for T:
T = 2000 / 5 = 400 K
Therefore, the triple point temperature of the substance is 400 K.
Phase Equilibrium Question 3:
The variation of molar heat capacity at constant volume (CV, m) with temperature (T) of a gaseous diatomic molecule is shown in the diagram below. The values of X, Y and Z, respectively, are
The diagram is not to the scale and discontinuity in the diagram represents dissociation]
Answer (Detailed Solution Below)
Phase Equilibrium Question 3 Detailed Solution
CONCEPT:
Variation of Molar Heat Capacity (CV,m) with Temperature for a Diatomic Gas
- Diatomic molecules exhibit contributions to heat capacity from different degrees of freedom as temperature increases:
- Translational motion: Always active → contributes (3/2)R
- Rotational motion: Becomes active at moderate temperatures → adds R ⇒ Total = 2.5 R
- Vibrational motion: Activates at higher temperatures → adds another R (from both potential and kinetic energy) ⇒ Total = 3.5 R
- The sharp jump (discontinuity) in the graph represents dissociation, beyond which CV can decrease due to bond breakage and energy redistribution.
EXPLANATION:
- At low T → only translational and rotational DOF contribute ⇒ X = 2.5 R
- At moderate T → vibrational modes begin to contribute ⇒ Y = 3.0 R
- At high T before dissociation is complete → full vibrational contribution ⇒ Z = 3.5 R
Therefore, the correct sequence is: X = 2.5 R, Y = 3.0 R, Z = 3.5 R — Option 2.
Phase Equilibrium Question 4:
The decomposition of CaCO3 in a closed vessel is represented by the equation
CaCO3(s)
Calculate the number of phases. components and degree of freedom
Answer (Detailed Solution Below)
Phase Equilibrium Question 4 Detailed Solution
Concept:
Phase Rule and Calculation of Phases, Components, and Degrees of Freedom
- The phase rule (Gibbs' phase rule) is a fundamental principle in thermodynamics that describes the relationship between the number of phases, components, and degrees of freedom in a system at equilibrium.
- The phase rule is given by the equation:
F = C - P + 2
where:- F is the degrees of freedom (the number of independent variables, such as temperature and pressure, that can be changed independently).
- C is the number of components (chemically independent substances in the system).
- P is the number of phases (distinct forms of matter present, such as solid, liquid, and gas).
Explanation:
- The decomposition of calcium carbonate (CaCO3) is represented by the reaction:
CaCO3(s) ⇌ CaO(s) + CO2(g)
- For this reaction:
- Number of phases (P): The system contains three phases—solid CaCO3, solid CaO, and gaseous CO2. Therefore, p = 3.
- Number of components (C): The components are CaCO3, CaO, and CO2. Thus, C = 2, because CaCO3 decomposes into CaO and CO2, making it two chemically independent components.
- Degrees of freedom (F): Using the phase rule equation:
F = C - P + 2
F = 2 - 3 + 2 = 1
Hence, the correct answer is P = 3; C = 2; F = 1.
Phase Equilibrium Question 5:
The number of phases in a system when calcium carbonate undergoes thermal decomposition
Answer (Detailed Solution Below)
Phase Equilibrium Question 5 Detailed Solution
Concept:
Phases in a System during Thermal Decomposition
The reaction is:
CaCO₃(s) → CaO(s) + CO₂(g)
- The number of phases in a system refers to the distinct states of matter (solid, liquid, gas) present in the system during a chemical process.
- When calcium carbonate undergoes thermal decomposition, it breaks down into calcium oxide and carbon dioxide gas.
- In this reaction, calcium carbonate (CaCO₃) is solid, calcium oxide (CaO) is also solid, and carbon dioxide (CO₂) is a gas. Therefore, the system contains three distinct phases: solid, solid, and gas.
Explanation:
- The decomposition of calcium carbonate involves solid calcium carbonate (CaCO₃) turning into solid calcium oxide (CaO) and gaseous carbon dioxide (CO₂).
- Thus, there are three phases in the system: solid (CaCO₃), solid (CaO), and gas (CO₂).
Therefore, the correct answer is: 3 phases.
Top Phase Equilibrium MCQ Objective Questions
Phase Equilibrium Question 6:
The decomposition of CaCO3 in a closed vessel is represented by the equation
CaCO3(s)
Calculate the number of phases. components and degree of freedom
Answer (Detailed Solution Below)
Phase Equilibrium Question 6 Detailed Solution
Concept:
Phase Rule and Calculation of Phases, Components, and Degrees of Freedom
- The phase rule (Gibbs' phase rule) is a fundamental principle in thermodynamics that describes the relationship between the number of phases, components, and degrees of freedom in a system at equilibrium.
- The phase rule is given by the equation:
F = C - P + 2
where:- F is the degrees of freedom (the number of independent variables, such as temperature and pressure, that can be changed independently).
- C is the number of components (chemically independent substances in the system).
- P is the number of phases (distinct forms of matter present, such as solid, liquid, and gas).
Explanation:
- The decomposition of calcium carbonate (CaCO3) is represented by the reaction:
CaCO3(s) ⇌ CaO(s) + CO2(g)
- For this reaction:
- Number of phases (P): The system contains three phases—solid CaCO3, solid CaO, and gaseous CO2. Therefore, p = 3.
- Number of components (C): The components are CaCO3, CaO, and CO2. Thus, C = 2, because CaCO3 decomposes into CaO and CO2, making it two chemically independent components.
- Degrees of freedom (F): Using the phase rule equation:
F = C - P + 2
F = 2 - 3 + 2 = 1
Hence, the correct answer is P = 3; C = 2; F = 1.
Phase Equilibrium Question 7:
The phase diagram of a single component system is given below.
The option with the correct number of degrees of freedom corresponding to the labelled points i, j, and k, respectively, is
Answer (Detailed Solution Below)
Phase Equilibrium Question 7 Detailed Solution
CONCEPT:
Degrees of Freedom in Phase Diagrams
F = C - P + 2
- The degrees of freedom (F) of a system can be calculated using the Gibbs phase rule:
- C is the number of components in the system (in this case, a single component system, so C = 1),
- P is the number of phases in equilibrium at the point in the phase diagram.
- At different points in a phase diagram, the number of phases (P) can vary, affecting the degrees of freedom.
EXPLANATION:
- For example:
- At point j, three phases meet (P = 3), so the system has zero degrees of freedom (F = 0).
- At point i, two phases meet (P = 2), so the system has one degree of freedom (F = 1).
- At point k, the system is in a single phase (P = 1), so the system has two degrees of freedom (F = 2).
- At point i (boundary between two phases), there is 1 degree of freedom because temperature and pressure can be varied independently.
- At point j (triple point where three phases meet), there are zero degrees of freedom because all variables (temperature and pressure) are fixed by the equilibrium of the three phases.
- At point k (single phase region), there are 2 degrees of freedom because both temperature and pressure can be varied independently.
Therefore, the degrees of freedom corresponding to points i, j, and k are 0, 1, and 2, respectively.
Phase Equilibrium Question 8:
The expressions for the vapour pressure of solid (𝑝1) and vapour pressure of liquid (𝑝2) phases of a pure substance, respectively, are
The triple point temperature of this substance is ____ K (in integer).
Answer (Detailed Solution Below) 400
Phase Equilibrium Question 8 Detailed Solution
CONCEPT:
Triple Point Temperature and Vapor Pressure Equality
ln(p1) = ln(p2)
- The triple point of a substance is the unique temperature and pressure at which all three phases (solid, liquid, and gas) coexist in equilibrium.
- At the triple point, the vapor pressure of the solid phase (p1) is equal to that of the liquid phase (p2):
- Given expressions:
- ln(p1) = -2000/T + 5
- ln(p2) = -4000/T + 10
EXPLANATION:
- At the triple point:
ln(p1) = ln(p2)
⇒ -2000/T + 5 = -4000/T + 10 - Rearranging terms:
-2000/T + 4000/T = 10 - 5
⇒ 2000/T = 5 - Solving for T:
T = 2000 / 5 = 400 K
Therefore, the triple point temperature of the substance is 400 K.
Phase Equilibrium Question 9:
The variation of molar heat capacity at constant volume (CV, m) with temperature (T) of a gaseous diatomic molecule is shown in the diagram below. The values of X, Y and Z, respectively, are
The diagram is not to the scale and discontinuity in the diagram represents dissociation]
Answer (Detailed Solution Below)
Phase Equilibrium Question 9 Detailed Solution
CONCEPT:
Variation of Molar Heat Capacity (CV,m) with Temperature for a Diatomic Gas
- Diatomic molecules exhibit contributions to heat capacity from different degrees of freedom as temperature increases:
- Translational motion: Always active → contributes (3/2)R
- Rotational motion: Becomes active at moderate temperatures → adds R ⇒ Total = 2.5 R
- Vibrational motion: Activates at higher temperatures → adds another R (from both potential and kinetic energy) ⇒ Total = 3.5 R
- The sharp jump (discontinuity) in the graph represents dissociation, beyond which CV can decrease due to bond breakage and energy redistribution.
EXPLANATION:
- At low T → only translational and rotational DOF contribute ⇒ X = 2.5 R
- At moderate T → vibrational modes begin to contribute ⇒ Y = 3.0 R
- At high T before dissociation is complete → full vibrational contribution ⇒ Z = 3.5 R
Therefore, the correct sequence is: X = 2.5 R, Y = 3.0 R, Z = 3.5 R — Option 2.
Phase Equilibrium Question 10:
The number of phases in a system when calcium carbonate undergoes thermal decomposition
Answer (Detailed Solution Below)
Phase Equilibrium Question 10 Detailed Solution
Concept:
Phases in a System during Thermal Decomposition
The reaction is:
CaCO₃(s) → CaO(s) + CO₂(g)
- The number of phases in a system refers to the distinct states of matter (solid, liquid, gas) present in the system during a chemical process.
- When calcium carbonate undergoes thermal decomposition, it breaks down into calcium oxide and carbon dioxide gas.
- In this reaction, calcium carbonate (CaCO₃) is solid, calcium oxide (CaO) is also solid, and carbon dioxide (CO₂) is a gas. Therefore, the system contains three distinct phases: solid, solid, and gas.
Explanation:
- The decomposition of calcium carbonate involves solid calcium carbonate (CaCO₃) turning into solid calcium oxide (CaO) and gaseous carbon dioxide (CO₂).
- Thus, there are three phases in the system: solid (CaCO₃), solid (CaO), and gas (CO₂).
Therefore, the correct answer is: 3 phases.
Phase Equilibrium Question 11:
The triangular coordinates for three - component system is given as
The mole fractions of xA, xB and xC for point e are :
Answer (Detailed Solution Below)
Phase Equilibrium Question 11 Detailed Solution
Concept:
Triangular Diagram for a Three-Component System
- A triangular diagram is used to represent the composition of a three-component system (A, B, and C) in terms of mole fractions.
- Each vertex of the triangle represents 100% of one component (xA, xB, or xC), while the opposite side corresponds to 0% of that component.
- The sum of the mole fractions of all three components at any point inside the triangle is always equal to 1:
xA + xB + xC = 1
Explanation:
- For point e on the diagram:
- The value of xA is determined by measuring the perpendicular distance from point e to the side opposite to vertex A. This value is approximately 0.20.
- The value of xB is determined by the perpendicular distance from point e to the side opposite to vertex B. This value is approximately 0.40.
- The value of xC is determined by the perpendicular distance from point e to the side opposite to vertex C. This value is also approximately 0.40.
- Hence, the mole fractions of xA, xB, and xC for point e are 0.20, 0.40, and 0.40, respectively.
Therefore, the correct answer is: 0.20, 0.40, 0.40.
Phase Equilibrium Question 12:
The number of degrees of freedom for liquid water and water vapour in equilibrium at a pressure of 1 atm is
Answer (Detailed Solution Below)
Phase Equilibrium Question 12 Detailed Solution
Concept:
Degrees of Freedom and Reduced Phase Rule
- The degrees of freedom (F) in a system are determined using Reduced Gibbs' Phase Rule:
F = C - P + 1
where:- F = degrees of freedom
- C = number of components
- P = number of phases in equilibrium
- This applies when considering a condensed system, where the pressure is essentially constant and the only relevant variables are temperature and composition, effectively reducing the number of degrees of freedom by one.
Explanation:
- System: Liquid water and water vapor are in equilibrium at 1 atm pressure.
- Number of components (C): The system has one component, H2O.
- Number of phases (P): Two phases are present: liquid and vapor.
- Calculation:
F = C - P + 1
F = 1 - 2 + 1
F = 0
Therefore, the number of degrees of freedom is: 0.