Chemical Properties p. 16 -21 Chapter 1 Section 3 Vocabulary: chemical property chemical change

Chemical Properties Chemical properties describe matter based on its ability to change into new matter that has different properties. For example, when wood is burned, ash and smoke are created. These new substances have very different properties than the original wood had. Wood has the chemical property of flammability. Flammability is the ability of a substance to burn. Ash and smoke can not burn, so they have the property of nonflammability. Another chemical property is reactivity. Reactivity is the ability of two or more substances to combine and form one or more new substances.

Reactivity with Oxygen

Comparing Physical and Chemical Properties You can observe physical properties without changing the identity of the substance. For example, rubbing alcohol is a clear liquid at room temp. Chemical properties aren’t as easy to observe. You can see that alcohol is flammable only when it is burning.

Characteristic Properties The properties that re most useful in identifying a substance are characteristic properties. These properties are always the same no matter what the sample is. Characteristic properties can be physical properties such as density and solubility, as well as chemical properties, such a flammability and reactivity. Scientists rely on characteristic properties to identify and classify substances.

Chemical Changes and New Substances A chemical change happens when one or more substances are changed into new substances that have new and different properties. CHEMICAL PROPERTIES AND CHEMICAL CHANGES ARE NOT THE SAME THING Chemical properties of a substance describe which chemical changes will and will not occur. For example, a substance has the ability to be flammable or nonflammable. Chemical changes are the process by which the substances actually change into new substances with new properties. For example, when a car burns gasoline, the gas actually changes into a new substance, water and air pollution.

Examples of Chemical Changes

Signs of a Chemical Change The number one sign that a chemical change has taken place is a new substance with totally new properties forms. Other signs that a chemical change has taken place are not quite as reliable every time. They are usually good indicators, but not always. These signs include: a change in color a change in odor production of light production of heat production of sound fizzing, foaming or bubbles forming not easily reversible

Physical vs. Chemical Changes The most important question to ask when trying to decide if a chemical or physical change has happened is, Did the substance change into a new substance with new properties? The new substance is nothing like the substances that originally made it up. If this is true, then you know that a chemical change has taken place. A chemical change alters the composition, or identity, of the substance. Physical changes do not change the identify of the original material. For example, water can be solid, liquid, or gas, and it looks very different in each of its forms, but its composition, or identity, remains the same.

Reversing Changes Many physical changes are easily reversed. They do not change the composition of the substance. For example, if you melt an ice cube, you could easily freeze the water to make another ice cube. Some physical changes are not as easily reversed. An example of this would be shaving wood into sawdust. You know the sawdust is still wood, but it is not easily reversed. The identity of the substance is still the same. In a chemical change, the composition of the substance changes into a new material with totally new properties. It would be almost impossible to reverse the chemical changes that happen when fireworks explode even if you collected all of the materials made in the chemical change. The only way to reverse a chemical change is with another chemical change, and even this would be difficult to do.

Chemical Changes Song

Quiz Time! 1. What does the term reactivity mean? It is the ability of two or more substances to combine and form one or more new substances. 2. How is a chemical change different from chemical properties? Chemical changes occur when one or more substances are changed into totally new substances with new properties. A chemical property tells whether a chemical change will happen. 3. Give an example of a chemical change that happens when you are cooking dinner. burning of gas when you cook in an oven or on the stove, cooking your food

4. What is the #1 sign that a chemical change has taken place? It forms a new substance with totally new properties. 5. List three other clues that a chemical change has taken place. color change, bubbles, fizzing, foaming, not easily reversible, new odor, heat, light or sound given off 6. Rusting is an example of a A. physical property B. physical change C. chemical property D. chemical change D