In a compound, two or more elements are joined chemically. For example, a mixture of tomatoes, lettuce, croutons, carrots, and raisins in a salad can be separated into its individual components. Many times, a mixture can be separated by a physical change into its individual substances. For example, if you mix salt with water, you get salty water. The properties of the mixture usually reflect the properties of the individual substances. In a mixture, two or more substances, elements, or compounds are combined physically. The concepts of physical and chemical change can be used to understand the differences between mixtures and compounds. There is no physical way to separate the rust back into iron and oxygen gas. When a piece of metal rusts, its color changes, because iron is chemically combining with oxygen from the air to form a new substance, rust. In a chemical change, such as rusting, the substances after the change are chemically different than the substances that were there before the change. The substances can be separated by scratching the wax off of the paper. When coloring a piece of paper with a crayon, crayon has been put on top of the paper, but the substances are still crayon wax and paper. In a purely physical change, the substances after the change are the same substances they were before the change. This can make it difficult to distinguish between a physical change that is purely physical and a physical change that is due to a chemical change. 1.6 A and B.Ĭhemical change is often accompanied by a physical change, such as a change in color. Examples of physical change are shown in Figs. Other examples of physical change are filtering, cutting, melting, and coloring the surface of something with paint, crayons, or markers. In each of the states, the chemical formula of water, H 2O, remains the same. Ice can melt to become a liquid, which can re-freeze back to a solid state. Physical changes can generally be reversed. Physical properties include taste, smell, texture, and color. In a physical change, the chemical formula of the substance remains the same, even though the physical properties may change. However, plasma is not a state of matter that is common or persistent in the natural world on earth.Ĭhanges between states of matter can be physical changes or chemical changes. Plasma can also be found on earth in thing like fluorescent lights and lightening. Plasma is very common in the universe, making up the stars and the space between the planets in our solar system. Plasma is a gas that is electrically charged. Many people think steam or clouds are water vapor, but they are actually tiny droplets of liquid water, not gaseous water. It is difficult to capture a photograph of water in a gaseous form. In a gas, the molecules of water are relatively far apart and are free to move at high speeds. As a gas, water vapor is free to move great distances through the atmosphere.In most other substances, the molecules of the solid are closer together than the molecules of the liquid (Fig. Re actually farther apart in the solid state than in the liquid state. Water is a unique substance because its molecules a In a solid, the molecules of water are relatively close together, but are held in a distinct shape. 1.5 A).Īs a solid, water takes a definite shape, as in a snowflake, ice cube, or glacier. In a liquid, the molecules of water are relatively close together and are free to move around each other (Fig.
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