The student is expected to: differentiate between physical and chemical changes and properties AND identify extensive and intensive properties AND classify matter as pure substances or mixtures through investigation of their properties AND compare solids, liquids, and gases in terms of compressibility, structure, shape, and volume.
A physical change to matter will not alter the composition or identity of a substance. A chemical change to matter will always result in the formation of a new substance.
The physical properties of matter include properties that describe the substance such as color, smell, boiling point, density, or others. The chemical properties of matter occur when matter goes through a specific chemical change.
Extensive properties of matter are properties that are dependent on the amount of a substance present, such as mass, number of particles, or energy. Intensive properties are physical properties of matter that are not dependent on the amount of a substance present such as density, ductility, and boiling point.
The fixed arrangement of the particles in a solid makes solids relatively incompressible. Liquids are more compressible than solids, but much less compressible than gases. Due to the wide spacing between particles, gases are very compressible.
All matter is composed of particles that are in constant motion. The particles in a solid have low energy and vibrate in fixed position. The particles in a liquid have higher energy and are able to move freely past each other. The particles in a gas are widely spaced with high energy and little attraction to each other.
Solids have a fixed shape due to the fixed arrangement of the particles. Liquids will take the shape of the container, as the particles are free to move past each other. Gases do not have a definite shape as the particles have a high degree of freedom to move past each other.
Solids and liquids will both have a definite volume. The volume of the solid is dependent on its shape. The volume of the liquid is dependent on its container. The volume of solids and liquids remains the same when placed in different containers because the space between the particles does not change. Gases will fill the volume of a closed container because the particles have little attraction and are widely spaced. If the container is opened, gases will not have a definite volume.
All matter on Earth can be classified as either a pure substance or a mixture. A pure substance consists of a single substance with its own definite composition and properties. A mixture consists of a combination of two or more pure substances with variable composition and properties.
Physical and Chemical Changes
In our daily life, we observe many different types of change activities such as dicing apples, cooking eggs, boiling water, and souring milk. Generally, these changes can be categorized into two types of changes known as physical changes and/or chemical changes. A physical change to matter will not alter the composition or identity of a substance. The molecules may be rearranged, but internal structures of the molecules will remain the same. However, a chemical change to matter will always result in the formation of a new substance. In order for a new substance to be formed, the chemical bonds between the atoms of the molecules must be broken and then reformed into new molecules.
Physical and Chemical Properties
The properties of matter are closely associated with the types of changes that matter goes through.
Chemical properties of matter include all of the possible chemical changes that a sample of matter can undergo. For instance, oxidation resistance (ability to resist corrosion), toxicity (the degree to which a substance is poisonous to an organism or the environment), and heat of combustion (amount of heat released when a substance is burned) are all chemical properties.
Physical properties of matter include properties that describe the substance, such as viscosity, color, melting point, smell, boiling point, or density. Measuring physical properties will not alter or change the chemical nature of substance as no bonds within the molecules would be broken. In addition, physical properties of a substance can be categorized as either an intensive property or an extensive property.
Extensive physical properties are physical properties of matter that depend on the amount of matter found within a substance. The amount of matter may be represented by mass, number of particles, or the amount of energy within the substance.
Intensive physical properties are physical properties of matter that do not depend on the amount of matter found within a substance. Instead, intensive properties depend on the type of matter found within a substance and are represented by properties such as density, ductility, and boiling point.
Comparing the States of Matter
Matter consists of molecules. Kinetic molecular theory states that all matter is composed of particles that are in constant motion. Solids, liquids, and gases are three different states, or phases, of matter. The corresponding behavior of molecules in each state of matter is what separates each type of state.
Solids: The particles in a solid have low energy and vibrate in fixed position. Solids have a fixed shape due to the fixed arrangement of the particles. The fixed arrangements of the particles in a solid make them relatively incompressible.
Liquids: The particles in a liquid have higher energy and are able to move freely past each other. Liquids will take the shape of the bottom of the container they are in, as the particles are free to move past each other. Liquids are more compressible than solids, but much less compressible than gases.
Gases: The particles in a gas are widely spaced with high energy and little attraction to each other. Gases do not have a definite shape, as the particles have a high degree of freedom to move past each other. Gases will expand to fill the (closed) container they are in. Due to the wide spacing between particles, gases are highly compressible.
Examples of Changing States of Matter
Water is the most common substance that we can easily observe in all three states of matter. In its solid state, water has a definite shape and structure and is incompressible. For example, an ice cube will remain in the shape of the container in which it was frozen and will shatter if hit with a hammer. Liquid water will take the shape of the bottom of the container that it is in, but it is still fairly incompressible. Gaseous water, or steam, will expand to fill a closed container, but has no specific shape or structure outside of the container. Due to the wide spacing between the particles, steam is highly compressible.
There are other examples of the variation between the solid, liquid, and gaseous states of matter. Solid sugar can be melted and turned into a thick liquid known as caramel. Propane, which exists in a liquid state when in a sealed tank under pressure, turns into a gas when the valve on the tank is opened. Cheese, which is normally in a solid state, turns to liquid that may flow freely when placed over heat. The smell of cooking food may travel from the kitchen to your nose as the gas molecules released from the cooking food travel freely throughout the house.
Comparing Volumes of Solids, Liquids, and Gases
As shown in the examples above, it is easy to understand why solids and liquids both have definite volume. The volume of the solid is dependent on its shape. The volume of the liquid is dependent on the bottom of its container. The volume of solids and liquids remains the same if placed in different containers as the space between the particles does not change. However, gases will fill the volume of a closed container as the particles are widely spaced and have little attraction to each other. If the container is opened, the gas will not keep a definite volume. In this way, gas has arbitrary shape.
Pure Substances and Mixtures
All matter on Earth can be classified as either a pure substance or a mixture.
Pure Substance: A pure substance consists of a single substance with its own definite composition and properties. Elements, such as gold and oxygen, are pure substances. Compounds, such as pure water, salt (sodium chloride), and carbon dioxide are also pure substances, as they have their own distinct physical and chemical properties.
Mixture: A mixture consists of a combination of two or more pure substances. Mixtures have variable composition and properties.
Heterogeneous mixtures have components that are not uniformly mixed or are in more than one phase. Examples of heterogeneous mixtures include beach sand, ice cubes in liquid water, or chicken soup. Suspensions are a special type of heterogeneous mixture. In suspensions, a portion of the particles suspended in that mixture will settle out upon standing. Examples include sand in water or dust particles in air.
Homogeneous mixtures have components that are uniformly mixed and are in only one phase. Homogeneous mixtures of liquids are called solutions. Examples include flour or completely dissolved salt water. The air that we breathe is also a mixture consisting of oxygen, nitrogen, and other inert gases. Colloids are a special type of homogeneous mixture in which the particles are indefinitely suspended in the medium. This medium may be a gas, a liquid, or a solid. Examples include clouds, blood, pearls, or paint.