1.3.2 - Definição de fase

Summary

The script discusses the concept of phases and mixtures, focusing on the behavior of pure substances in different physical states (liquid, solid). It explains that a single pure substance in one state constitutes one phase, but multiple states (such as liquid and solid) lead to multiple phases. The video also explores various types of mixtures, including homogeneous mixtures like water and ethanol, and explains the solubility limits in solutions like water and salt. Additionally, the concept of gas mixtures and solid solutions, such as metal alloys, is covered, emphasizing the homogeneity and phase formation in different substances.

Takeaways

• 😀 A substance is considered to have one phase when it is in a single physical state, but if it exists in multiple physical states, there will be multiple phases.
• 😀 Water is an example of a substance that can exist in different phases (liquid and solid), each with distinct properties due to the different molecular arrangements.
• 😀 A homogeneous mixture consists of only one phase, where the substances are uniformly distributed.
• 😀 A heterogeneous mixture involves more than one phase, with distinct boundaries between substances.
• 😀 The solubility limit is the maximum amount of a substance (like salt) that can dissolve in a solvent (like water) without forming a precipitate.
• 😀 Water can dissolve a certain amount of salt (35.9g per 100mL at 25°C) before it reaches the solubility limit, beyond which the excess salt will precipitate.
• 😀 Gaseous mixtures, such as air and NO2, always form a single homogeneous phase because gases can freely mix and disperse throughout a container.
• 😀 Solid solutions, like metal alloys (e.g., copper and nickel), involve substances that can dissolve into each other in any proportion without forming separate phases.
• 😀 In a solid solution, the atoms of the substances involved (like copper and nickel) are so similar that they form a single, uniform structure at the atomic level.
• 😀 The concept of solid solutions can also apply to other materials, such as iron-carbon alloys, where carbon can dissolve in iron until a certain limit, beyond which phase separation occurs.

Q & A

What is the relationship between a pure substance and a phase?

A pure substance corresponds to a single phase only if it is in one physical state. For example, water in a single phase can be in the liquid or solid state, but as long as it is in one state, it remains a single phase. If the substance transitions to another physical state, multiple phases can coexist.

How does the molecular arrangement differ in liquid and solid states of water?

In the liquid state, water molecules are more spread out, allowing them to flow and interact freely. In the solid state (ice), the molecules are more tightly packed and organized into a crystalline structure, which gives it a different set of physical properties.

What defines a homogeneous mixture?

A homogeneous mixture consists of only one phase, meaning its components are uniformly distributed throughout. This uniformity means that no distinct boundaries between components are observed.

Can you give an example of a homogeneous mixture in liquid form?

An example of a homogeneous mixture in liquid form is a solution of water and ethanol. No matter the proportion of each, the two liquids mix uniformly without separation of phases.

What is the concept of solubility limit?

The solubility limit refers to the maximum amount of a substance that can dissolve in a solvent at a given temperature. If the solvent reaches this limit, any excess solute will no longer dissolve and will precipitate out of the solution.

How does the solubility of salt in water work?

When salt is added to water, the salt particles dissolve, but there is a limit to how much can dissolve. If more salt is added beyond the solubility limit (e.g., 35.9 grams per 100 mL at 25°C), excess salt will remain undissolved and form a solid deposit at the bottom of the container.

How does gas mixing differ from liquid or solid mixtures?

When gases mix, they always form a single homogeneous phase. This is because gas molecules move freely and occupy the entire volume of the container, mixing evenly with other gases without forming distinct phases.

What happens when you allow two different gases to mix in separate containers?

When two different gases are allowed to mix by opening a valve between their separate containers, their molecules will disperse evenly across both containers. This results in a single homogeneous phase throughout both containers.

What is a solid solution, and how does it relate to alloys?

A solid solution occurs when two or more substances dissolve in each other in the solid state, forming a homogeneous structure. An example is a metal alloy, like a copper-nickel mixture, where both metals dissolve into each other uniformly, without forming separate phases.

What is the significance of the solubility limit in a metal alloy?

In metal alloys, such as a copper-nickel mixture, the solubility limit determines how much of one metal can dissolve in the other. Beyond this limit, the excess metal may precipitate out, and the alloy will contain more than one phase.