Changes of state Transitional Reasoning Download PDF

Questions

1. 1.

   An experimenter heats a pure solid sample at a constant power input inside an insulated container. While the substance remains at its constant melting temperature, it takes 3 minutes to melt completely, but at its boiling temperature, it requires 21 minutes under the same heating rate to vaporize completely. Which statement correctly explains why vaporizing this substance requires substantially more thermal energy than melting the same mass?

   • A) Vaporization requires thermal energy to break the strong intramolecular bonds within each molecule, whereas melting only disrupts weaker intermolecular attractions between molecules.
   • B) Vaporization involves a continuous increase in the average kinetic energy of the particles, whereas melting occurs at a constant temperature without any kinetic energy changes.
   • C) Melting requires energy only to loosen the rigid lattice while particles remain in close contact, whereas vaporization requires overcoming nearly all intermolecular attractions to separate particles to large distances.
   • D) Vaporization must perform large mechanical work to compress the surrounding air, whereas melting requires no work because the liquid expands into the open container.
2. 2.

   During an experiment investigating phase transitions, a student fills a transparent syringe with pure water at 65 °C, expels all air, and tightly caps the nozzle. When the plunger is rapidly pulled outward to expand the internal space, vigorous bubbling begins throughout the liquid volume despite no external heat being added. Which statement correctly explains why this change of state occurs and describes the thermal energy change of the remaining liquid?

   • A) The reduced pressure matches the vapor pressure of water at 65 °C to cause boiling, which absorbs latent heat from the liquid and lowers its temperature.
   • B) The rapid expansion of volume transfers mechanical work to the molecules, raising their kinetic energy until the water reaches its normal 100 °C boiling point.
   • C) The sudden drop in pressure forces dissolved air to escape as bubbles, releasing latent heat of condensation that warms the liquid.
   • D) The decrease in external pressure compresses the liquid particles into a denser state, releasing potential energy that maintains boiling at a constant temperature.
3. 3.

   During cold snaps when overnight temperatures drop slightly below 0 °C, citrus growers routinely spray their orchards with a fine mist of liquid water. As a thin layer of ice forms over the branches and fruit, the delicate plant tissues are successfully shielded from freezing injury. Which statement correctly explains the thermal mechanism responsible for protecting the fruit during this phase change?

   • A) Freezing is an endothermic phase transition that absorbs thermal energy from the frigid atmosphere, creating a protective thermal barrier around the plant tissue.
   • B) Freezing increases the average kinetic energy of the water molecules, which transfers sensible heat into the plant tissue until the ice completely forms.
   • C) Freezing is an exothermic phase transition that releases latent heat of fusion to the plant tissue, holding its temperature near 0 °C as long as water continues to solidify.
   • D) Freezing traps ambient thermal radiation inside the liquid layer, preventing latent heat from escaping into the colder surrounding air.
4. 4.

   In an experiment to investigate energy transfer during phase changes, a student introduces 5 g of steam at 100 °C into an insulated calorimeter containing 100 g of water at 20 °C, while adding 5 g of liquid water at 100 °C into an identical calorimeter setup. Upon reaching thermal equilibrium, the mixture receiving the steam records a substantially higher final temperature than the mixture receiving the boiling liquid. Based on particle interactions and energy changes during phase transitions, which statement correctly explains this observation?

   • A) Steam particles at 100 °C possess significantly greater average kinetic energy than liquid water particles at the same temperature.
   • B) Condensing steam releases latent heat as intermolecular bonds form, transferring substantial additional thermal energy before cooling as a liquid.
   • C) Liquid water absorbs thermal energy from the calorimeter to break surface tension forces, suppressing its final equilibrium temperature.
   • D) Gaseous water molecules have a lower density, allowing them to transfer kinetic energy via buoyant convection without thermal dissipation.
5. 5.

   A student wraps the sensor of a digital thermometer with cotton gauze saturated with a volatile pure liquid at an ambient room temperature of 21 °C. Over the next several minutes, the thermometer reading decreases to 15 °C while the liquid evaporates, remaining depressed until the gauze dries completely and slowly returns to 21 °C. Based on particle behavior during changes of state, which statement correctly explains the cause of this observed temperature decrease?

   • A) Evaporation causes the liquid particles to draw cold energy from the surrounding environment as they expand into gas.
   • B) The transition from liquid to gas destroys thermal energy inside the liquid to create space between the separating particles.
   • C) Ambient gas molecules colliding with the wet gauze lose kinetic energy, transferring their cold temperature directly to the liquid.
   • D) Particles with kinetic energy higher than the average overcome intermolecular forces and escape, lowering the mean kinetic energy of the remaining liquid.
6. 6.

   A block of solid carbon dioxide is placed on an open balance inside a laboratory room at 22 °C. Over several minutes, the mass reading steadily decreases without any liquid residue forming on the pan, while a dense white mist appears in the air immediately around the block. Based on these observations, which statement correctly identifies the phase changes taking place and explains their thermal behavior?

   • A) The solid carbon dioxide undergoes evaporation by releasing thermal energy, which causes airborne dust and gaseous carbon dioxide to form a visible vapor.
   • B) The solid carbon dioxide melts directly into a fine liquid spray by absorbing thermal energy, which raises the temperature of the air and prevents condensation.
   • C) The solid carbon dioxide undergoes deposition by absorbing thermal energy from the air, which causes atmospheric nitrogen to condense into visible clouds.
   • D) The solid carbon dioxide undergoes sublimation by absorbing thermal energy from the surroundings, which cools the adjacent air and causes ambient water vapor to condense into tiny liquid droplets.
7. 7.

   A student investigates phase transitions by placing two identical metal containers in a room with humid air at 22 °C. Container 1 is filled with a freezing mixture at -10 °C, and firm crystalline frost forms directly on its exterior without any liquid appearing. Container 2 is filled with water at 12 °C, resulting only in liquid droplets collecting on its exterior. Which statement correctly identifies the phase transition responsible for the frost on Container 1 and describes the thermal energy transfer that occurs during this process?

   • A) The phase transition is deposition, during which water vapor releases thermal energy to the cold container as it transforms into solid ice.
   • B) The phase transition is sublimation, during which water vapor absorbs thermal energy from the cold container as it transforms into solid ice.
   • C) The phase transition is deposition, during which water vapor absorbs thermal energy from the cold container to organize into a solid structure.
   • D) The phase transition is freezing, during which an invisible liquid film rapidly releases thermal energy to the container to form ice.
8. 8.

   A student investigates vaporization by observing two beakers containing equal volumes of pure water under identical atmospheric pressure. In Beaker X, maintained at 60 °C, the liquid volume slowly decreases over time without any bubbling, while in Beaker Y, maintained at 100 °C, vapor bubbles continuously form at the heated base and rise through the liquid. Which statement correctly distinguishes the phase change mechanisms occurring in the two beakers?

   • A) In Beaker X, the transition involves the release of trapped atmospheric gases, whereas in Beaker Y, heat creates vapor exclusively at the top surface of the liquid.
   • B) In Beaker X, evaporation occurs only at the exposed surface where energetic particles escape, whereas in Beaker Y, boiling occurs throughout the liquid as vapor pressure matches atmospheric pressure.
   • C) In Beaker X, intermolecular forces are unchanged during the transition, whereas in Beaker Y, covalent bonds within the water molecules are broken to form gaseous bubbles.
   • D) In Beaker X, thermal energy is converted directly into potential energy across the bulk, whereas in Beaker Y, bubbles form because the liquid temperature rises continuously above 100 °C.
9. 9.

   A student continuously supplies heat at a constant rate to a beaker containing a pure solid while monitoring its temperature. Between the fourth and eighth minutes, the substance progressively melts into a liquid, yet the thermometer reading stays constant at 55 °C throughout this transition. Which statement correctly explains why the temperature does not rise during this change of state?

   • A) The transferred thermal energy is fully absorbed by the container walls, temporarily halting heat transfer to the substance.
   • B) The supplied thermal energy is used to overcome intermolecular attractions rather than increasing the average kinetic energy of the particles.
   • C) The particles vibrate faster and gain kinetic energy, but the volumetric expansion of the liquid cancels out the temperature increase.
   • D) The thermal energy is consumed by breaking covalent bonds within the molecules, converting the sample into different chemical substances.