Questions: Phase Diagrams
20 Multiple-Choice Questions: Phase Diagrams
Questions:
1. What does a phase diagram represent?
A) The rate of a chemical reaction
B) The solubility of a compound
C) The states of matter at different temperatures and pressures
D) The chemical composition of a compound
E) The electron configuration of an element
2. Which phase is present at high temperature and low pressure in a typical phase diagram?
A) Solid
B) Liquid
C) Gas
D) Plasma
E) Bose-Einstein Condensate
3. What does the line separating two phases on a phase diagram indicate?
A) A change in mass
B) A chemical reaction
C) Equilibrium between the two phases
D) A constant volume
E) The end of a phase
4. What is the triple point?
A) Where three compounds react
B) The point of maximum density
C) Where solid, liquid, and gas coexist
D) The boiling point of water
E) Where gas turns directly into solid
5. Which condition describes the critical point?
A) Maximum pressure only
B) Temperature and pressure where liquid and gas are indistinguishable
C) Where solid and liquid phases meet
D) Lowest melting point
E) Beginning of boiling
6. What happens to a substance beyond the critical point?
A) It freezes
B) It decomposes
C) It forms a supercritical fluid
D) It evaporates
E) It condenses
7. Which phase transition is represented by a line between solid and gas on a phase diagram?
A) Melting
B) Boiling
C) Sublimation
D) Condensation
E) Freezing
8. The area under the solid region of a phase diagram typically lies at:
A) Low pressure and high temperature
B) High pressure and high temperature
C) Low pressure and low temperature
D) High pressure and low temperature
E) Any pressure and high temperature
9. In most substances, the slope of the solid-liquid equilibrium line is:
A) Negative
B) Vertical
C) Positive
D) Horizontal
E) Parabolic
10. Water has a unique phase diagram because:
A) It cannot exist as a solid
B) Its solid-liquid line has a negative slope
C) Its triple point is at absolute zero
D) It has no critical point
E) Its boiling point never changes
11. A point inside the gas region of the diagram indicates:
A) Coexistence of solid and liquid
B) Only solid present
C) Only gas is stable
D) Mixture of phases
E) Phase is undefined
12. What does the term "supercritical fluid" mean?
A) Gas that behaves like a plasma
B) Solid with high compressibility
C) Fluid with properties of both liquid and gas
D) Frozen gas
E) Non-existent phase
13. In a phase diagram, increasing pressure generally:
A) Favors the gas phase
B) Favors the liquid or solid phase
C) Converts liquids into gases
D) Has no effect
E) Lowers the boiling point
14. A solid turning directly into a gas without becoming a liquid is called:
A) Condensation
B) Deposition
C) Sublimation
D) Evaporation
E) Melting
15. Which of the following is an example of sublimation?
A) Ice melting
B) Water boiling
C) Dry ice turning to gas
D) Water freezing
E) Steam condensing
16. Which variable is plotted on the x-axis of a typical phase diagram?
A) Volume
B) Density
C) Pressure
D) Temperature
E) Mass
17. What is the phase present at very low temperature and very high pressure?
A) Gas
B) Supercritical fluid
C) Liquid
D) Solid
E) Plasma
18. On a phase diagram, where is the boiling point of a substance found?
A) At the triple point
B) Along the solid-gas line
C) On the solid-liquid line
D) On the liquid-gas equilibrium line
E) Beyond the critical point
19. What phase change occurs along the liquid-gas line?
A) Melting
B) Boiling or condensation
C) Freezing
D) Sublimation
E) Deposition
20. Why is the triple point significant?
A) It defines standard temperature
B) It marks maximum boiling
C) It is required to calculate molar mass
D) It is the only set of conditions where all three phases coexist
E) It indicates maximum density
- Questions on Change of State of Matter
- Questions on Condensation
- Questions on Heating and Cooling Curves
Extended Answers and Explanations:
1. C) The states of matter at different temperatures and pressures
→ A phase diagram maps physical states of a substance under varying pressure and temperature.
2. C) Gas
→ At high temperatures and low pressures, substances typically exist in the gas phase.
3. C) Equilibrium between the two phases
→ The boundary lines show conditions where two phases coexist in equilibrium.
4. C) Where solid, liquid, and gas coexist
→ At the triple point, all three phases are in equilibrium.
5. B) Temperature and pressure where liquid and gas are indistinguishable
→ This is the definition of the critical point.
6. C) It forms a supercritical fluid
→ Beyond the critical point, the substance becomes a supercritical fluid, having properties of both gas and liquid.
7. C) Sublimation
→ Direct transition from solid to gas without passing through the liquid phase.
8. D) High pressure and low temperature
→ Solids are typically favored under these conditions.
9. C) Positive
→ In most substances, as pressure increases, the melting point increases (positive slope).
10. B) Its solid-liquid line has a negative slope
→ Ice melts under pressure, a unique behavior shown by the negative slope.
11. C) Only gas is stable
→ The gas region shows where gas is the only stable phase.
12. C) Fluid with properties of both liquid and gas
→ Supercritical fluids behave like both liquids and gases.
13. B) Favors the liquid or solid phase
→ Higher pressure pushes molecules closer, favoring condensed states.
14. C) Sublimation
→ This is the phase change from solid directly to gas.
15. C) Dry ice turning to gas
→ Solid CO₂ sublimates at atmospheric pressure.
16. D) Temperature
→ Standard phase diagrams have temperature on the x-axis.
17. D) Solid
→ These conditions typically result in the solid phase.
18. D) On the liquid-gas equilibrium line
→ Boiling occurs along this boundary.
19. B) Boiling or condensation
→ These transitions happen on the liquid-gas line.
20. D) It is the only set of conditions where all three phases coexist
→ This is a unique feature of the triple point.
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