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Slide 1 of 19 Chemistry. © Copyright Pearson Prentice Hall Slide 2 of 19 Chemical Reactions Iron is abundant, easy to shape when heated, and relatively.

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Presentation on theme: "Slide 1 of 19 Chemistry. © Copyright Pearson Prentice Hall Slide 2 of 19 Chemical Reactions Iron is abundant, easy to shape when heated, and relatively."— Presentation transcript:

1 Slide 1 of 19 Chemistry

2 © Copyright Pearson Prentice Hall Slide 2 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

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

4 Slide 4 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

5 © Copyright Pearson Prentice Hall Slide 5 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

6 Slide 6 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

7 Slide 7 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

8 Slide 8 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

9 Slide 9 of 19 © Copyright Pearson Prentice Hall Chemical Reactions > Question! Is a change in phase a physical or a chemical change? Explain ans. It Is a physical change the composition does not change.

10 Slide 10 of 19 © Copyright Pearson Prentice Hall Chemical Reactions > Question! Iron and oxygen combine to form iron oxide List the reactants and the products Ans. Fe + O  Fe 2 O 3 reactants Products

11 © Copyright Pearson Prentice Hall Chemical Reactions > Slide 11 of 19 Recognizing Chemical Changes 2.4 Recognizing Chemical Changes What are four possible clues that a chemical change has taken place?

12 © Copyright Pearson Prentice Hall Slide 12 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

13 Slide 13 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

14 © Copyright Pearson Prentice Hall Chemical Reactions > Slide 14 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?

15 © Copyright Pearson Prentice Hall Slide 15 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.

16 Slide 16 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

17 Slide 17 of 19 © Copyright Pearson Prentice Hall Chemical Reactions > Question! A 13.0 g sample of X combines with a 34.0 g sample of Y to form the compound XY 2. What is the mass of the reactants? Ans g

18 Slide 18 of 19 © Copyright Pearson Prentice Hall Chemical Reactions > Question! Sodium Chloride can be formed by the reaction of sodium metal and chlorine gas. If 45.98g of sodium combines with an excess of chlorine gas to form g sodium chloride, what mass of chlorine gas is used in the reaction? Ans: 2Na + Cl 2  2NaCl 45.98g X g g g = 70.91g of chlorine

19 Slide 19 of 19 © Copyright Pearson Prentice Hall Chemical Reactions > Question! Which of the following are the same and which are different? A.A substance and a pure substance B. a heterogeneous mixture and a solution C. a substance and a mixture D.A homogeneous mixture and a solution Ans. A and d same b and c different

20 © Copyright Pearson Prentice Hall Slide 20 of 19 Section Quiz -or- Continue to: Launch: Assess students’ understanding of the concepts in Section 2.4 Section Quiz. 2.4.

21 © Copyright Pearson Prentice Hall Slide 21 of Section Quiz. 1.Which of the following is a chemical reaction? a.melting of lead b.dissolving sugar in water c.rusting of iron d.crushing of stone

22 © Copyright Pearson Prentice Hall Slide 22 of 19 2.Which of the following is NOT a possible clue that a chemical change is taking place? a.a change of state b.a change in color c.production of a gas d.formation of a precipitate 2.4 Section Quiz.

23 © Copyright Pearson Prentice Hall Slide 23 of 19 3.During any chemical change, the mass of the products is a.always equal to the mass of the reactants. b.always greater than the mass of the reactants. c.always less than the mass of the reactants. d.sometimes different than the mass of the reactants. 2.4 Section Quiz.

24 © Copyright Pearson Prentice Hall Slide 24 of 19 Chemical Reactions > Concept Map 2 Concept Map 2 Solve the Concept Map with the help of an interactive guided tutorial.

25 © Copyright Pearson Prentice Hall Slide 25 of 19 Chemical Reactions > Homework Page 55 #49-55

26 © Copyright Pearson Prentice Hall Slide 26 of 19 Chemical Reactions > Questions! page 59 58, ( do not copy table), 66, 67, 68, 70

27 END OF SHOW

28 Homework Page 58 # 49-54


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