INTRODUCTION

Relevance of the Theme

"State Changes" is a central theme in the study of matter and physics. With this understanding, it becomes possible to explain everyday phenomena such as water boiling, ice melting, vapor condensation, among others. Furthermore, the study of state changes is fundamental for the comprehension of more advanced topics, such as thermodynamics and quantum theory. Therefore, this theme is an important milestone in this learning journey, and its implications reverberate throughout the scientific spectrum.

Contextualization

"State Changes" are strongly linked to the study of states of matter, which is a preceding topic in your school curriculum. During the development of this subject, you will understand the defining properties of each state of matter (solid, liquid, gas) and how energy can alter these states. This discussion also lays the groundwork for future topics, such as atomic and molecular structure, and how particles in a system interact with each other. Thus, by exploring "State Changes," you are embarking on an interconnected journey in the vast and incredible area of the science of matter.

THEORETICAL DEVELOPMENT

Components

• States of Matter: All matter existing in the universe can be classified into three states: solid, liquid, and gas. In this first subtopic, we will review the characteristics of each state, such as the rigidity of solids, the fluidity of liquids, and the compressibility of gases.

  • Solid: Characterized by having a fixed shape and volume, due to the regular structural organization of the particles (atoms, molecules, or ions) that compose it. The particles in this state have low kinetic energy, meaning they have vibrational motion.

  • Liquid: Has a fixed volume but takes the shape of the container it is in. This occurs due to the mobility of the particles, which have a greater degree of freedom of movement than in the solid state. The particles in the liquid state have disordered flow.

  • Gaseous: Does not have a fixed shape or volume, expanding to fill all available space. The particles (atoms or molecules) in this state have completely disordered and high-speed motion.

• State Changes: A "state change" is the transformation that occurs in matter when there is an increase or decrease in the energy of its particles. The three main state changes are:

  • Fusion: Transition from the solid state to the liquid state, which occurs with an increase in the system's energy. The temperature at which this change occurs is known as the "melting point."

  • Vaporization: Transformation from the liquid state to the gaseous state, again through an increase in energy. The specific temperature at which this occurs is the "boiling point."

  • Condensation: Change from the gaseous state to the liquid state, occurring when the gas loses thermal energy. The "condensation point" is the corresponding temperature.

Key Terms

• Latent Heat: Is the amount of energy that a gram of a substance needs to change state, at constant pressure. This concept is essential to understand state changes.

• Thermal Energy: Is the energy related to the temperature of a system. In state changes, thermal energy is added or removed for them to occur.

• Phase Diagram: Is a graphical representation that shows under which conditions (temperature and pressure) a given substance exists in each state of matter. It is a valuable tool for understanding state changes.

Examples and Cases

• "Why Does Clothes Dry?": This example illustrates the state change of a substance in everyday conditions. The water in wet fabric changes from a liquid state to a gaseous state through the process of evaporation, when the thermal energy from the sun is absorbed by the water.

• "From Fire to Steam": Here, we use the example of heating water in a kettle. As thermal energy is added, the water undergoes successive state changes: from cold (solid) to hot (liquid) and finally to very hot (gaseous).

• "The Magic of Dry Ice": Carbon dioxide in the solid state (dry ice) does not pass through the liquid state when heated, but rather directly to the gaseous state in a process called sublimation. This example helps us understand that state changes do not necessarily follow a strict order.

DETAILED SUMMARY

Key Points

• States of Matter: Three main states (solid, liquid, and gas) with distinct characteristics that depend on the level of organization and energy of their constituent particles.

• State Change and Energy: Energy is fundamental in the occurrence of state changes. The addition of energy results in transitions to states with greater disorder and, therefore, greater particle mobility. The removal of energy promotes the reverse process.

• Latent Heat: Key concept that describes the amount of energy needed for a unit of mass of a substance to change its state, at constant pressure. It varies according to the substance and the state in question.

• Phase Diagram: Useful graphical representation to visualize and interpret state changes. It shows how temperature and pressure influence the state of matter.

Conclusions

• Interdependence of States and Energy: Understanding how energy affects the states of matter is crucial to understanding state changes.

• Importance of Latent Heat: This concept demonstrates that the temperature of a substance does not change during a state change, but the system's energy does.

• Versatility of State Changes: Demonstrated by the example of dry ice. The substance transitions directly from the solid state to the gaseous state, without passing through the liquid state.

Exercises

1. Describe what happens to the particles (atoms, molecules, ions) during the fusion of a solid material, specifying how their energy changes.

2. Why does the temperature of liquid water not change during the boiling process?

3. Give an example of a material that, when heated, changes directly from a solid to a gas, without passing through the liquid state. Explain the physical phenomenon involved, paying attention to the concept of energy.