Physical Properties of & Changes in Matter

An attribute, quality, or characteristic of a substance that distinguishes it from another are called properties.

Scientists define matter as anything that has mass and takes up space (or has volume). 

• Mass is a fundamental property of matter that measures the amount (number of particles) of substance in an object. 

• The basic SI (International System of Units) unit of mass is the kilogram (kg). 

Volume measures (quantifies) the amount of space occupied by an object or substance in three-dimensional space. Volume is a derived quantity because it's calculated based on the dimensions of an object's length, width, and height.

In the context of physical sciences and materials, a property of something refers to a characteristic or attribute that can be used to describe or quantify that thing. Properties provide information about how an object or substance behaves, what it's composed of, and how it interacts with other substances or forces. Properties are essential for understanding and categorizing matter.

Any characteristic of matter that can be measured, and is not associated with a change in its chemical composition.

• • Mass: The amount of matter in an object.

  • Volume: The amount of space an object occupies.

  • Density: Mass per unit volume.

  • Color: The visual appearance of an object.

  • Texture: How an object feels to the touch.

  • Melting Point: The temperature at which a solid turns into a liquid.

  • Boiling Point: The temperature at which a liquid turns into a gas.

  • Conductivity: The ability to conduct heat or electricity.

  • Magnetism: The property of being attracted to a magnet.

  • Hardness: The resistance to being scratched or dented.

A physical change is a type of change in which the physical properties of a substance are altered without changing its chemical composition. During a physical change, the substance undergoes a transformation in its state, shape, size, or phase but remains the same substance with the same chemical composition. No new substances are formed, and the change is usually reversible.

Key characteristics of physical changes include:

• No Change in Chemical Composition: The fundamental chemical structure of the substance remains unchanged. The substance is composed of the same types and numbers of atoms or molecules before and after the change.

• Reversibility: In most cases, physical changes are reversible, meaning you can return the substance to its original state by reversing the conditions or processes that caused the change. For example, if you melt ice (solid water) to obtain liquid water, you can reverse the change by cooling the liquid water to freeze it back into ice.

• Changes in Physical Properties: Physical changes involve alterations in the substance's physical properties, such as its state of matter (solid, liquid, gas), shape, size, density, color, or phase (e.g., melting, freezing, boiling, condensing).

Matter can be changed from one state to another through the addition or removal of energy, typically in the form of heat. The process of changing matter from one state to another is called a phase transition. The three primary states of matter are solid, liquid, and gas.

Traditionally, there are three primary states of matter:

• Solid: In the solid state, particles are closely packed together in a highly ordered, fixed pattern. Solids have a definite shape and volume. The particles in a solid vibrate in place, but they do not move past each other to any significant extent.
• Liquid: In the liquid state, particles are still closely packed, but they are not held in a rigid, ordered arrangement like in a solid. Liquids have a definite volume but take the shape of their container. Particles in a liquid have more freedom to move past one another compared to solids.
• Gas: In the gas state, particles are widely spaced apart and have high kinetic energy. Gases have neither a definite shape nor a definite volume and take the shape and volume of their container. Particles in a gas move rapidly and freely, colliding with each other and the container walls.

These are the three classical states of matter that we encounter in everyday life. However, there are also other, less common states of matter that can exist under specific conditions:

• Plasma: Plasma is often considered the fourth state of matter. It consists of highly energized particles, such as ions and free electrons, and is typically found at very high temperatures. Plasma is characterized by its ability to conduct electricity and respond to electromagnetic fields. Examples of plasma include stars like the Sun and fluorescent lights.

Melting an ice cube is considered a reversible physical change because it involves a transition from the solid state (ice) to the liquid state (liquid water) without altering the chemical composition of the substance. In this process, the ice molecules remain as water molecules, consisting of H2O. The reversibility of this change is primarily due to the fact that it is driven by changes in temperature.

When a piece of wood is ground into sawdust, that change is irreversible since the sawdust could not be reconstituted into the same piece of wood that it was before.

These phase transitions are governed by the principles of thermodynamics, which describe how energy influences the behavior of matter. The temperature and pressure conditions, as well as the nature of the substance, play critical roles in determining the specific phase transition that occurs.

• Melting (Solid to Liquid): Changing a solid into a liquid is called melting. This transition occurs when you add heat to a solid substance. The heat provides enough energy to the particles in the solid to overcome the attractive forces holding them in a rigid structure. As a result, the solid particles gain enough kinetic energy to move more freely and become a liquid.
• Freezing (Liquid to Solid): The reverse process of melting is freezing. When you remove heat from a liquid, the particles lose kinetic energy, slow down, and come together to form a more ordered and structured arrangement, transitioning into a solid.
• Vaporization (Liquid to Gas): Vaporization includes two processes:
• Evaporation: This is a gradual process in which the surface molecules of a liquid gain enough energy to escape into the surrounding air as vapor. It occurs at temperatures below the boiling point.
• Boiling: Boiling is a rapid process in which the entire volume of a liquid reaches its boiling point, and vapor bubbles form throughout the liquid. Boiling occurs at a specific temperature for each substance, known as the boiling point.
• Condensation (Gas to Liquid): When you cool a gas, its particles lose kinetic energy and come closer together, forming a liquid. This process is known as condensation. It's the reverse of vaporization.
• Sublimation (Solid to Gas): Sublimation is a phase transition in which a solid directly transforms into a gas without passing through the liquid phase. This happens when the solid's vapor pressure exceeds atmospheric pressure at a given temperature. Dry ice (solid carbon dioxide) is an example of a substance that undergoes sublimation at room temperature.
• Deposition (Gas to Solid): Deposition is the reverse of sublimation. It occurs when a gas changes directly into a solid without becoming a liquid first. This process is responsible for the formation of frost on surfaces in cold environments.

Physical properties of matter can be classified as either extensive or intensive. These classifications depend on whether the property is dependent on the amount or size of the substance (extensive) or if it remains constant regardless of the quantity of the substance (intensive).

Extensive properties vary according to the amount of matter present. 

• Examples of extensive properties include mass, volume, and length.

Extensive Properties:

• Mass: Mass is an extensive property because it depends on the amount of substance present. Larger quantities of a substance have greater mass.
• Volume: Volume is also an extensive property. It relates to the amount of space a substance occupies, and larger quantities of a substance have greater volume.
• Length: Length is an extensive property because it depends on the size or extent of the object. Longer objects have greater length.
• Total Energy: The total energy of a system, such as the thermal energy of an object, is an extensive property. It is proportional to the amount of matter present.
• Total Charge: The total charge of a system is extensive because it depends on the quantity of charged particles (e.g., electrons, protons) present.

Intensive Properties:

• Density: Density is an intensive property because it remains constant regardless of the amount of substance. It is the ratio of mass to volume and provides information about the substance's compactness.
• Temperature: Temperature is an intensive property that indicates the average kinetic energy of particles in a substance. It is the same whether you have a small or large quantity of the substance.
• Color: Color is an intensive property that describes the visual appearance of a substance and is independent of quantity.
• Melting Point: Melting point is an intensive property. It is the temperature at which a substance changes from a solid to a liquid state and does not depend on the quantity of the substance.
• Boiling Point: Boiling point is also an intensive property. It is the temperature at which a substance changes from a liquid to a gas and is constant regardless of the amount of substance.
• Density: Density is an intensive property because it relates mass and volume and is the same for a given substance regardless of the quantity.
• Intensive properties are particularly useful for identifying and characterizing substances because they provide information about the inherent nature of the material, while extensive properties are more influenced by the amount or size of the substance.