Table of Contents

1. Table of Contents • Observing Chemical Change • Describing Chemical Reactions • Controlling Chemical Reactions • Fire and Fire Safety

2. - Observing Chemical Change Properties and Changes in Matter • Matter can undergo both physical change and chemical change.

3. - Observing Chemical Change Energy in Chemical Changes • A student places two substances in a flask and measures the temperature once per minute while the substances react. The student plots the time and temperature data and creates the graph at left.

4. At 4 minutes the temperature in the flask was about 23ºC. The first time the temperature was 6ºC was at about 7 minutes. Reading Graphs: What was the temperature in the flask at 4 minutes? When was the first time the temperature was at 6ºC? - Observing Chemical Change Energy in Chemical Changes

5. 20ºC Calculating: How many degrees did the temperature drop between2 minutes and 5 minutes? - Observing Chemical Change Energy in Chemical Changes

6. The reaction was endothermic; it absorbed thermal energy from the reaction mixture, causing the temperature to drop. Interpreting Data: Is the reaction endothermic or exothermic? Explain. - Observing Chemical Change Energy in Chemical Changes

7. The reaction stopped at about 2ºC. You can tell because that is the lowest temperature reached. Inferring: At what temperature did the reaction stop? How can you tell? - Observing Chemical Change Energy in Chemical Changes

8. If the temperature increased, the reaction would be exothermic; an exothermic reaction is one in which energy is released. Drawing Conclusions: Suppose the temperature in the flask increased instead of decreased as the reaction occurred. In terms of energy, what kind of reaction would it be? Explain. - Observing Chemical Change Energy in Chemical Changes

9. - Observing Chemical Change Asking Questions • Before you read, preview the red headings. In a graphic organizer like the one below, ask a what or how question for each heading. As you read, write answers to your questions. Properties and Changes of Matter Question Answer What are physical properties of matter? Physical properties are characteristics that can be observed without changing one substance into another. What is the evidence for chemical reactions? The evidence for chemical reactions is the formation of new substances and changes in energy.

10. - Observing Chemical Change Links on Chemical Changes • Click the SciLinks button for links on chemical changes.

11. End of Section:Observing Chemical Change

12. Learning Objectives • Apply the principle of the conservation of mass to chemical reactions (in other words, balance chemical equations correctly). • Identify what a chemical equation contains (with an example). • Explain what a balanced chemical equation must show. • Identify the 4 main types of chemical reactions. (Synthesis tomorrow)

13. Conservation of Mass Demo (NO Lab Write-up) • Goal- Determine if mass was conserved (remained constant) for the reaction of copper (II) sulfate with sodium hydroxide to form copper (II) hydroxide: Cu(OH)2. • Data: Mass before = ? • Mass After = ? • Conclusion: Was mass conserved? How do you know?

14. - Describing Chemical Reactions Conservation of Mass • The principle of conservation of mass states that in a chemical reaction, the total mass of the reactants must equal the total mass of the products. This is why we must balance chemical equations (because mass is conserved)!

15. Conservation of Mass Review • For the reaction A + B AB, which masses are equal? • Mass of A = Mass of B • Mass of B = Mass of AB • Mass of A = Mass of AB • Mass of A + Mass of B = Mass of AB

16. - Observing Chemical Change Properties and Changes in Matter • Chemical reactions occur when bonds break and new bonds form.

17. - Describing Chemical Reactions Describing Chemical Reactions • Cellular phone messages make use of symbols and abbreviations to express ideas in shorter form. Similarly, chemists often use chemical equations in place of words.

18. - Describing Chemical Reactions What Are Chemical Equations? • Chemical equations use chemical formulas and other symbols instead of words to summarize a reaction.

19. - Describing Chemical Reactions Chemical Formulas • The formula of a compound identifies the elements in the compound and the ratios in which their atoms are present.

20. - Describing Chemical Reactions Balancing Chemical Equations • Magnesium metal (Mg) reacts with oxygen gas (O2), forming magnesium oxide (MgO). To write a balanced equation for this reaction, first write the equation using the formulas of the reactants and products, then count the number of atoms of each element.

21. Balancing Chemical Equations • Mg + O2 MgO

22. - Describing Chemical Reactions Balancing Chemical Equations • To describe a reaction accurately, a chemical equation must show the same number of each type of atom on both sides of the equation (due to the principle of the conservation of matter).

23. Balancing Equations Practice • K + I2 KI • Na + H2O NaOH + H2 • AgNO3 + K2S KNO3 + Ag2S • CuSO4 + NaOH Na2SO4 + Cu(OH)2

24. Noggin Knockers

25. Synthesis Reaction Experiment • Goals: Observe and write the balanced chemical equations for 2 synthesis reactions, and identify a synthesis reaction. • Procedure: Given verbally. Do NOT touch the penny, tongs, or burner after heating! Only put a pre-1982 penny in the flame! • Results: Observations of the penny after heating (but before you place it in the water) and after placing the penny in the water. • Conclusion: Write the balanced equations for both reactions and describe the characteristics of a synthesis reaction. (Products: Red = Cu2O, Dull black = CuO)

26. Synthesis Reaction • Multiple (more than 1) reactantscombining to form 1product. • Example: Copper metal combining with oxygen gas to form copper (II) oxide… • 2Cu + O22CuO

27. Synthesis Reaction Review • Identify all of the following chemical equations that represent a synthesis reaction: • Mg + O2 2MgO • AB A + B • A + B AB • A + BC AC + B • CuCl2 + Al AlCl3 + Cu

28. Balancing Chemical Equations for Synthesis Reactions • Na + Cl2 NaCl • Balance the equation for the reaction of sodium metal (Na) with oxygen gas (O2), forming sodium oxide (Na2O). • P + Cl2 PCl3 • N2 +H2 NH3

29. Ratios in Chemical Equations • There’s a 2 to 1 ratio of hydrogen gas (H2) to oxygen gas (O2) that produces 2water molecules (H2O). • What’s the ratio of oxygen gas (O2) to water (H2O)? • 1 to 2 + Energy

30. Noggin Knockers

31. Decomposition Reactions • Goals: Observe and write the balanced chemical equations for 2 decomposition reactions (one from the demo), and identify this type of reaction. • Procedure: Heat up a piece of chalk (CaCO3) in the burner flame for at least 5 minutes. Then place the chalk in the cup with water and observe what happens. • Results: Observations of the chalk after heating (but before you place it in the water) and after placing the chalk in the water. • Conclusions: Write the balanced equations for both reactions (one is from the demo) and describe the characteristics of a decomposition reaction.

32. Balancing Equations (Decomposition Reactions)

33. Decomposition Reactions • Only 1 reactant, but multiple products (more than 1). • XY X + Y

34. Balancing Chemical Equations (Decomposition): Describe the last one in words & include the number of each molecule- Ion chart on p. 23 • HgO Hg + O2 • KClO3 KCl + O2 • NaHCO3 Na2CO3 + H2O + CO2

35. Noggin Knockers

36. Single Replacement Reactions • Goals: Observe and write the balanced chemical equations for 3 single replacement reactions (3 from the demos), and identify this type of reaction. • Procedure: Place the iron nail into the blue solution of copper (II) sulfate. Take it out after a few seconds. • Results: Observations of the nail before and after placing it in the copper (II) sulfate solution. • Conclusions: Write the balanced equations for BOTH reactions (including the one from the demo) and describe the characteristics of a single replacement reaction.

37. Balancing Equations • Demo 1: • Demo 2:

38. Balancing Equations • Demo 3 (Thermite):

39. Single Replacement Reaction • One element (or type of atom) replaces another in a compound. • XY + Z XZ + Y • Analogy:

40. Noggin Knockers

41. Double Replacement Reactions • Goals: Observe and write the balanced chemical equations for 6 double replacement reactions (5 from the lab and 1 from the video), and identify this type of reaction. • Procedure: Place 3-5 drops of the following solutions in their own well (in the chem. plate): Magnesium sulfate (MgSO4), Nickel chloride (NiCl2),Copper (II) sulfate (CuSO4),Iron (III) chloride (FeCl3), & Cobalt chloride (CoCl2). Then add 3-5 drops of the sodium silicate solution (Na2SiO3) to form metal silicates and stir with the clean end of a toothpick. Disposal- scoop out solids and put them in the trash and wipe the plate clean. WASH hands immediately if you get any chemical on them! • Results: Observations of each reaction in terms of what formed. You may want to write down your observationsunder the chemical formula for the compound that formed in the equation for each reaction. • Example: Al2(SiO3)3 • Conclusions: Write the balanced equations for all reactions (including one from the video) and describe the characteristics of a double replacement reaction. white

42. Balancing Equations (Silicate ion = SiO3-2) • Na2SiO3 + MgSO4 MgSiO3 + Na2SO4 • Na2SiO3 + FeCl3 Fe2(SiO3)3 + NaCl • Na2SiO3 + CuSO4 CuSiO3 + Na2SO4 • Na2SiO3 + NiCl2 NiSiO3 + NaCl • Na2SiO3 + CoCl2 CoSiO3 + NaCl

43. - Describing Chemical Reactions Classifying Chemical Reactions • Double Replacement reactions involve 2 types of atoms (or groups of atoms) switching places in different compounds. • AB + CD AD + BC

44. Double Replacement Reaction (Video)

45. Balancing Equations (Silicate ion = SiO3-2) • Na2SiO3 + MgSO4 MgSiO3 + Na2SO4 • Na2SiO3 + FeCl3 Fe2(SiO3)3 + NaCl • Na2SiO3 + CuSO4 CuSiO3 + Na2SO4 • Na2SiO3 + NiCl2 NiSiO3 + NaCl • Na2SiO3 + CoCl2 CoSiO3 + NaCl

46. For a single replacement reaction… • Two types of atoms switch places between compounds. • One type of atom replaces another in a compound. • There are always 2 reactants and 1 product. • There is only one reactant.

47. Which of the following represents a single replacement reaction? • AB A + B • AB + CD AD + BC • AB + C AC + B • A + B AB

48. Which of following only shows copper (Cu) being replaced by silver (Ag)? • 2Ag + CuSO4 Ag2SO4 + Cu • Ag + Cu AgCu • CuCl2 Cu + Cl2 • CuSO4 + 2AgNO3 Cu(NO3)2 + Ag2SO4

49. How can you tell if a chemical reaction is a decomposition reaction? • If there’s 2 or more products. • If there’s 2 or more reactants. • If there’s only 1 reactant. • If there’s only 1 product.

50. Why are synthesis and decomposition reactions considered opposites? • They both have only one reactant. • Synthesis reactions have 2 products while decomposition reactions have only 1 product. • They’re not opposites. • Synthesis reactions have only 1 product while decomposition reactions have only 1 reactant.