Changes of state Knowledge-Based Download PDF

Questions

1. 1.

   How does the presence of a dissolved impurity affect the freezing point of a pure liquid at constant atmospheric pressure?

   • A) It increases the freezing point.
   • B) It decreases the freezing point.
   • C) It keeps the freezing point unchanged.
   • D) It eliminates the freezing process entirely.
2. 2.

   Which of the following changes will decrease the rate of evaporation of a liquid held in an open container?

   • A) Increasing the temperature of the liquid
   • B) Increasing the relative humidity of the surrounding air
   • C) Increasing the surface area of the exposed liquid
   • D) Increasing the speed of air moving across the liquid surface
3. 3.

   In a closed container maintained at a constant temperature, under which condition does a liquid achieve dynamic phase equilibrium with its vapor?

   • A) When the liquid has completely converted into the gaseous state
   • B) When the mass of the vapor becomes equal to the mass of the remaining liquid
   • C) When molecules in both phases cease all kinetic motion and energy exchange
   • D) When the rate of evaporation equals the rate of condensation
4. 4.

   When a gas condenses into a liquid at constant temperature, how do the average kinetic energy of its molecules and its intermolecular potential energy change?

   • A) The average kinetic energy decreases, while the intermolecular potential energy remains constant.
   • B) The average kinetic energy remains constant, while the intermolecular potential energy increases.
   • C) The average kinetic energy remains constant, while the intermolecular potential energy decreases.
   • D) The average kinetic energy decreases, while the intermolecular potential energy decreases.
5. 5.

   When liquid water freezes to become solid ice at 0 °C under atmospheric pressure, how do its volume and density change?

   • A) Its volume decreases and its density increases.
   • B) Its volume increases and its density decreases.
   • C) Both its volume and its density decrease.
   • D) Both its volume and its density increase.
6. 6.

   Why does exposure to steam at 100 °C cause significantly more severe burns to human skin than exposure to an equal mass of liquid water at 100 °C?

   • A) Steam possesses a significantly higher temperature than boiling water under atmospheric pressure.
   • B) Steam releases a large quantity of latent heat as it condenses into liquid water on the cooler skin.
   • C) Steam has a much higher specific heat capacity than liquid water once thermal contact is made.
   • D) Steam transfers thermal energy faster because gas particles penetrate deeply into dermal tissue.
7. 7.

   For a pure substance at a given constant external pressure, how does its freezing point compare to its melting point?

   • A) The freezing point is significantly lower than the melting point.
   • B) The freezing point is slightly higher than the melting point.
   • C) The freezing point depends on the cooling rate, whereas the melting point is completely fixed.
   • D) The freezing point occurs at the same temperature as the melting point.
8. 8.

   Which of the following statements correctly explains why the evaporation of a liquid results in the cooling of the remaining liquid?

   • A) Molecules at the surface transfer their kinetic energy directly to the surrounding air through conduction.
   • B) The formation of vapor creates a localized drop in pressure that forces the remaining liquid to contract.
   • C) Molecules with the lowest kinetic energy leave the surface first, lowering the internal energy of the liquid.
   • D) Molecules with the highest kinetic energy overcome intermolecular forces and escape, decreasing the average kinetic energy of the remaining liquid.
9. 9.

   How does an increase in external pressure affect the boiling point of a liquid?

   • A) The boiling point decreases because the liquid requires less thermal energy to overcome the external pressure.
   • B) The boiling point increases because a higher vapor pressure is required to equal the external pressure.
   • C) The boiling point remains unchanged because the boiling temperature depends solely on chemical composition.
   • D) The boiling point decreases because intermolecular forces become weaker under elevated pressure.
10. 10.

    In a heating curve of a pure substance heated at a constant rate, in which sections does the average kinetic energy of the particles increase?

    • A) In the horizontal plateaus where melting and boiling take place
    • B) Throughout all sections equally because heat is supplied at a constant rate
    • C) Only during the phase change from liquid to gas
    • D) In the sloped sections where the temperature of a single phase increases
11. 11.

    Why is the specific latent heat of vaporization of a substance generally much larger than its specific latent heat of fusion?

    • A) Melting requires completely separating molecules against attractive forces, whereas vaporization only disrupts their ordered arrangement.
    • B) Vaporization requires overcoming intermolecular attractive forces to separate molecules completely, whereas melting only weakens the bonds between them.
    • C) The average kinetic energy of the molecules increases significantly during vaporization, but remains constant during fusion.
    • D) Vaporization occurs over a wide range of temperatures, whereas fusion can only take place at a single fixed temperature.
12. 12.

    What physical quantity is defined as the amount of thermal energy required to change a unit mass of a substance from a solid to a liquid without any change in temperature?

    • A) Specific heat capacity
    • B) Latent heat of vaporization
    • C) Thermal conductivity
    • D) Latent heat of fusion
13. 13.

    Under which condition does a liquid begin to boil at a constant atmospheric pressure?

    • A) When the rate of evaporation from the surface decreases to zero
    • B) When the density of the liquid becomes equal to the density of the surrounding air
    • C) When thermal energy ceases to transfer between the liquid and its heat source
    • D) When the saturated vapor pressure of the liquid equals the external atmospheric pressure
14. 14.

    At the microscopic level, what happens to the molecules of a pure liquid as it undergoes boiling at constant atmospheric pressure?

    • A) The covalent bonds within each molecule break, separating the liquid into constituent atoms.
    • B) The average kinetic energy of the molecules increases continuously as thermal energy is absorbed.
    • C) The molecules overcome attractive intermolecular forces, increasing their potential energy while their average kinetic energy remains constant.
    • D) The molecules slow down and form rigid bonds to fill the entire container uniformly.
15. 15.

    Which of the following statements correctly describes a key difference between evaporation and boiling?

    • A) Boiling occurs exclusively at the exposed surface of the liquid, whereas evaporation takes place throughout the entire bulk.
    • B) Evaporation requires the liquid to reach a fixed boiling point, whereas boiling can occur at any temperature.
    • C) Evaporation takes place only at the exposed surface of the liquid, whereas boiling occurs throughout the bulk of the liquid with bubble formation.
    • D) Evaporation increases the average kinetic energy of the remaining liquid, whereas boiling always decreases it.
16. 16.

    Which term describes the phase change in which a substance transitions directly from a gas to a solid without passing through the liquid state?

    • A) Sublimation
    • B) Condensation
    • C) Deposition
    • D) Vaporization
17. 17.

    Which of the following changes of state releases thermal energy to the surroundings?

    • A) Melting
    • B) Condensation
    • C) Evaporation
    • D) Sublimation
18. 18.

    What happens to the temperature of a pure crystalline solid while it is undergoing melting at constant pressure?

    • A) It remains constant because absorbed energy is used to overcome intermolecular forces rather than increase kinetic energy.
    • B) It increases steadily because absorbed energy directly raises the average kinetic energy of the particles.
    • C) It decreases temporarily because thermal energy is consumed to initiate the phase change.
    • D) It fluctuates unpredictably because solid and liquid phases cannot coexist at a stable temperature.