# Phase Transition Questions and Answers

Practice Phase Transition Questions and Answers.

## Phase Transition Questions and Answers

Q1. Identity which one is a first order phase transition ?

• (a) A liquid to gas transition at its critical temperature
• (b) A liquid to gas transition close to its triple point
• (c) A paramagnetic to ferromagnetic transition in the absence of a magnetic field
• (d) A metal to superconductor transition in the absence of a magnetic field

Q2. Consider the transition of liquid water to steam as water boils at a temperature of 100°C under a pressure of 1 atmosphere. Which one of the following quantities does not change discontinuously at the transition ?

• (a) The Gibbs free energy
• (b) The entropy
• (c) The internal energy
• (d) The specific volume

Q3. A quantity of water is completely converted into steam by boiling :

• (a) This is a second order phase transition
• (b) At the boiling point, the chemical potential in the vapour phase is less than that in the liquid phase.
• (c) The boiling temperature would increased if the boiling were done under increased pressure.
• (d) The entropy of the steam is less than that of the water.

Q4. Identify which one is a first order phase transition ?

• (a) A liquid to gas transition at its critical temperature
• (b) A liquid to gas transition close to its triple point
• (c) A paramegnetic to ferromagnetic transition in the absence of a magnetic field.
• (d) A metal to superconductor transition in the absence of a magnetic field.

Q5. Which of the following is an example of a first order phase transition ?

• (a) A liquid – gas phase transition at the critical point.
• (b) A paramagnet – ferromagnet phase transition
• (c) A normal metal- superconductor phase transition
• (d) A liquid – gas phase transition away from the critical point

Q6. Which one of the following is a first order phase transition ?

• (a) vaporization of a liquid at its boiling point
• (b) ferromagnetic to paramagnetic
• (c) normal liquid He to superfluid He
• (d) superconducting to normal state

Q7. In a first order phase transition, at the transition temperature, specific heat of the system

• (a) Diverges and its entropy remains the same
• (b) Diverges and its entropy has finite discontinuity.
• (c) Remains unchanged and its entropy has finite discontinuity.
• (d) Has finite discontinuity and its entropy diverges.

Q8. Across a first order phase transition, the free energy is

• (a) proportional to the temperature
• (b) a discontinuous function of the temperature
• (c) a continuous function of the temperature but its derivative is discontinuous
• (d) such that the first derivative with respect to temperature is continuous

Q9. A second order phase transition is one in which

• (a) the plot of entropy as a function of temperature shows a discontinuity.
• (b) the plot of specific heat as a function of temperature shows a discontinuity
• (c) the plot of volume as a function of pressure shows a discontinuity
• (d) the plot of compressibility as a function of temperature is continuous.

Q10. The transition from ordinary liquid helium (He – I) to superfluid helium (He – II) is an example of a second order lambda point transition. The quantities that remain constant in such a transition at the transition point are

• (a) entropy, volume, specific heat at constant pressure and Gibbs free energy
• (b) pressure, volume and isothermal compressibility.
• (c) specific heat at constant pressure, isothermal compressibility and pressure
• (d) pressure, volume, entropy and Gibbs free energy

Q11. The pressure versus temperature diagram of a given system at certain low temperature range is found to be parallel to the temperature axis in the liquid to solid transition region The change in the specific volume remains constant in this region. The conclusion one can get from the above is

• (a) the entropy of solid is zero in this temperature region the entropy increases when
• (b) the system goes from liquid to solid phase in this temperature region
• (c) the entropy decreases when the system transforms from liquid to solid phase in this region
• (d) the change in entropy is zero in the liquid to solid transition region

Q12. For a liquid to vapour phase transition at Ttr which of the plots between specific Gibbs free energy ‘g’ and temperature T is correct ?

Q13. When two phases 1 and 2 of a system are in thermodynamic equilibrium, their temperature T, pressure p and chemical potential μ satisfy

• (a) T1 = T2 , P1 = P2 and μ1 = μ2
• (b) T1 = T2 , P1 = P2 and μ1 ≠ μ2
• (c) T1 = T2 ,  μ1 = μ2 and P1 ≠ P2
• (d) T1 = T2 but P1 ≠ P2 , μ1 ≠ μ2

Q14. The vapour pressure (p), in mm of Hg. of solid ammonia is given by the relation: In p = 23.01 -(3754/T), where T is the absolute temperature. The vapour pressure, in mm of Hg, of liquid ammonia is given by the relation In p = 19.49 – (3063/T). The temperature of the triple point is about

• (a) 191.3 K
• (b) 196.3 K
• (c) 206.3 K
• (d) 296.3 K

Q15. The ratio (∂V/∂T)p ,  is negative for

• (a) Ice at 0°C
• (b) Water at 100°C
• (c) Water at 10°C
• (d) Water between 0°C and 4°C

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