When a substance changes from one phase to another, which of the following occurs?
the substance loses or gains heat
the average kenetic energy of the substance changes
the temperature of a substance changes
the molecular motion of a substance changes
You know 1 is true because of heat fusion and heat vaporization.
You know 3 is not true since melting or boiling take place AT a particular temperature rather than through a particular range of temperatures.
Look at the other two and see what you think.
It is the last one. I chose the 2nd one and got it wrong.
When a substance changes from one phase to another, such as from solid to liquid or from liquid to gas, all of the following usually occur:
1. The substance loses or gains heat: To change phases, energy is required to break the intermolecular forces holding the particles together. When transitioning from a solid to a liquid or from a liquid to a gas, heat is usually added to the substance to provide the energy required for the phase change. Conversely, when transitioning from a gas to a liquid or from a liquid to a solid, heat is usually released from the substance.
2. The average kinetic energy of the substance changes: In different phases, the particles of a substance have different arrangements and levels of motion. As a substance changes phases, the average kinetic energy of its particles changes. For example, in the solid phase, the particles vibrate in fixed positions, whereas in the liquid or gas phases, the particles have greater freedom of movement and higher kinetic energy.
3. The temperature of the substance changes: During a phase change, the temperature of the substance remains constant until the entire phase change is complete. Once the phase change is finished, the substance's temperature can start changing again. This occurs because the energy added or released during the phase change affects the particles' potential energy, not their kinetic energy, which is related to temperature.
4. The molecular motion of the substance changes: As a substance changes phases, the arrangement and motion of its molecules or particles also change. In a solid, the particles are closely packed in a regular pattern, whereas in a liquid, they are still in close contact but can move around more freely. In a gas, the particles are spread out and move independently, with more random motion.
It's important to note that these changes are general observations and can vary depending on the substance and specific conditions. Additionally, all of these changes are interconnected, meaning one change often affects the others.