1. © Copyright Pearson Prentice Hall Slide 1 of 19 Chemical Reactions Iron is abundant, easy to shape when heated, and relatively strong, especially when mixed with carbon in steel. Over time, objects made of iron will rust if they are left exposed to air. You will learn to recognize chemical changes and to distinguish them from physical changes. 2.4

2. © Copyright Pearson Prentice Hall Chemical Reactions > Slide 2 of 19 2.4 3 Chemical Changes What always happens during a chemical change?

3. Slide 3 of 19 © Copyright Pearson Prentice Hall Chemical Reactions > Chemical Changes The ability of a substance to undergo a specific chemical change is called a chemical property. Chemical properties can be used to identify a substance. But chemical properties can be observed only when a substance undergoes a chemical change. 2.4

4. © Copyright Pearson Prentice Hall Slide 4 of 19 Chemical Reactions > Chemical Changes During a chemical change, the composition of matter always changes. Recall that during a physical change, the composition of matter never changes. 2.4

5. Slide 5 of 19 © Copyright Pearson Prentice Hall Chemical Reactions > Chemical Changes A magnet separates iron from sulfur. This is an example of a physical change. 2.4

6. Slide 6 of 19 © Copyright Pearson Prentice Hall Chemical Reactions > Chemical Changes A mixture of iron and sulfur is heated. The iron and sulfur react and form iron sulfide. This is an example of a chemical change. 2.4

7. Slide 7 of 19 © Copyright Pearson Prentice Hall Chemical Reactions > Chemical Changes A chemical change is also called a chemical reaction. One or more substances change into one or more new substances during a chemical reaction. A substance present at the start of the reaction is a reactant. A substance produced in the reaction is a product. 2.4

8. © Copyright Pearson Prentice Hall Chemical Reactions > Slide 8 of 19 Recognizing Chemical Changes 2.4 Recognizing Chemical Changes What are four possible clues that a chemical change has taken place?

9. © Copyright Pearson Prentice Hall Slide 9 of 19 Chemical Reactions > Recognizing Chemical Changes Possible clues to chemical change include: a transfer of energy a change in color the production of a gas the formation of a precipitate. 2.4

10. Slide 10 of 19 © Copyright Pearson Prentice Hall Chemical Reactions > Chemical Changes A precipitate is a solid that forms and settles out of a liquid mixture. Clues to chemical changes have practical applications. 2.4

11. © Copyright Pearson Prentice Hall Chemical Reactions > Slide 11 of 19 Conservation of Mass 2.4 Conservation of Mass How are the mass of the reactants and the mass of the products of a chemical reaction related?

12. © Copyright Pearson Prentice Hall Slide 12 of 19 Chemical Reactions > Conservation of Mass 2.4 During any chemical reaction, the mass of the products is always equal to the mass of the reactants.

13. Slide 13 of 19 © Copyright Pearson Prentice Hall Chemical Reactions > Conservation of Mass The law of conservation of mass states that in any physical change or chemical reaction, mass is conserved. The conservation of mass is easily observed when a change occurs in a closed container. 2.4

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