Chemical Reactions Occur in Predictable Ways

1. Chemical Reactions Occur in Predictable Ways Chapter 6

2. What You Will Learn • Classifying reactions as one of six different types • Synthesis (Combination) Reactions • Decomposition Reactions • Single Replacement Reactions • Double Replacement Reactions • Neutralization (Acid-Base) Reactions • Combustion Reactions

3. What You Will Learn • To predict the IDENTITY OF PRODUCTS of a chemical reaction • To identify factors that affect the RATE of a chemical reaction • To Define the RATE of a chemical reaction • To explain role of CATALYSTS in a chemical reaction

4. Chapter 6 Assignment • Assignment to be handed in as 1 package on test day: • Workbook complete • Check your understanding Page 271 *odds • Check your understanding Page 281 *odds • Chapter Review – Checking Concepts 1-4

5. Chapter 6 Project • Making graphic organizers for 2 main concepts • Page 282 – Prepare your own summary section *choose only 2 • Page 583 – Graphic organizers *must have 2 different types • Venn diagram, Concept map, Spider Map, Flowchart, Cycle Chart etc… *choose 2 • Choose 2 of the following, • Six types of Chemical reactions • Classifying and predicting Products of Reactions Based on the Reactants Only • Examples of Reactions Occurring at Different Rates • Four Factors Affecting the Rates of Reactions

6. 6.1 Types of Chemical Reactions DID YOU KNOW??… All known chemical reactions require energy to break the chemical bonds in the reactants. Energy is often released when new bonds form in the products.

7. LAB 6-1A Comparing Chemical Reactions • Lose marks for safety, clean up, focus, professionalism, and procedural issues. • Full marks for being engaged, safe, respectful, and a best effort attempt. • Due at end of class.

8. Steps to Writing Reactions • Some steps for doing reactions • Identify the type of reaction • Predict the product(s) using the type of reaction as a model • Balance it Don’t forget about the diatomic elements! (BrINClHOF) For example, Oxygen is O2 as anelement.

9. 1. Synthesis reactions • Synthesis reactions occur when two substances (generallyelements) combine and form a compound. (Sometimes these are called combination or addition reactions.) reactant + reactant  1 product • Basically: A + B  AB • Example: 2H2 + O2  2H2O • Example: C+ O2  CO2

10. Synthesis Reactions 2K(g) + Cl2 (g) 2KCl (s) Potassium + Chlorine ?

11. Practice • Predict the products. Write and balance the following synthesis reaction equations. • Sodium metal reacts with chlorine gas Na(s) + Cl2(g)  • Solid Magnesium reacts with fluorine gas Mg(s) + F2(g)  • Aluminum metal reacts with fluorine gas Al(s) + F2(g) 

12. 2. Decomposition Reactions • Decomposition reactions occur when a compound breaks up into the elements or into a few simpler compounds • 1 Reactant  Product + Product • In general: AB  A + B • Example: 2 H2O  2H2 + O2 • Example: 2 HgO  2Hg + O2

13. Decomposition Reactions 2HgO(s) 2Hg(l) + O2(g) What is in this example?

14. Decomposition Exceptions FYI • Carbonates and chlorates are special case decomposition reactions that do not go to the elements. • Carbonates (CO32-) decompose to carbon dioxide and a metal oxide • Example: CaCO3  CO2 + CaO • Chlorates (ClO3-) decompose to oxygen gas and a metal chloride • Example: 2 Al(ClO3)3  2 AlCl3 + 9 O2

15. Practice • Predict the products. Then, write and balance the following decomposition reaction equations: • Solid Lead (IV) oxide decomposes PbO2(s)  • Aluminum nitride decomposes AlN(s) 

16. Practice Identify the type of reaction for each of the following synthesis or decomposition reactions, and write the balanced equation: N2(g) + O2(g) BaCO3(s)  Co(s)+ S(s)  NH3(g) + H2CO3(aq)  NI3(s)  Nitrogen monoxide (make Co be +3)

17. 3. Single Replacement Reactions • Single Replacement Reactions occur when one element replaces another in a compound. • A metal can replace a metal (+) OR a nonmetal can replace a nonmetal (-). • element + compound element + compound A + BC  AC + B (if A is a metal)OR A + BC  BA + C (if A is a nonmetal) (remember the cation always goes first!) When H2O splits into ions, it splits into H+ and OH- (not H+ and O-2 !!)

18. Single Replacement Reactions 2Li(s) + 2H2O(l) 2LiOH(aq) + H2 (g) Lithium is a metal.

19. Single Replacement Reactions • Write and balance the following single replacement reaction equation: • Zinc metal reacts with aqueous hydrochloric acid Zn(s) + HCl(aq) ZnCl2 + H2(g) Note: Zinc replaces the hydrogen ion in the reaction 2

20. Single Replacement Reactions • Sodium chloride solid reacts with fluorine gas NaCl(s) + F2(g)  NaF(s) + Cl2(g) Note that fluorine replaces chlorine in the compound Is the equation balanced? • Aluminum metal reacts with aqueous copper (II) nitrate Al(s)+ Cu(NO3)2(aq)

21. 4. Double Replacement Reactions • Double Replacement Reactions occur when a metal replaces a metal in a compound and a nonmetal replaces a nonmetal in a compound • Compound + compound  compound+ compound • AB + CD  AD + CB

22. Double Replacement Reactions • Think about it like “foil”ing in algebra, first and last ions go together + inside ions go together • Example: AgNO3(aq) + NaCl(s)  AgCl(s) + NaNO3(aq) • Another example: K2SO4(aq) + Ba(NO3)2(aq)  KNO3(aq) + BaSO4(s) 2

23. Practice • Predict the products. Balance the equation • HCl(aq) + AgNO3(aq)  • CaCl2(aq) + Na3PO4(aq)  • Pb(NO3)2(aq) + BaCl2(aq)  • FeCl3(aq) + NaOH(aq)  • H2SO4(aq) + NaOH(aq)  • KOH(aq) + CuSO4(aq) 

24. Neutralization (Acid-Base) Reactions • When an acid and base are mixed they will neutralize each other. • An acid and base react to form a salt and water. • Acid + Base Salt + Water • HX + MOH MX + H2O • X represents a negative ion - M represents a positive ion • Practice problems on page 263

25. 5. Combustion Reactions • Combustion reactions occur when a hydrocarbon reacts with oxygen gas. • This is also called burning!!! In order to burn something you need the 3 things in the “fire triangle”:1) A Fuel (hydrocarbon)2) Oxygen to burn it with3) Something to ignite the reaction (spark)

26. Combustion Reactions • In general: CxHy+ O2  CO2 + H2O • Products in combustion are ALWAYS carbon dioxide and water. (although incomplete burning does cause some by-products like carbon monoxide) • Combustion is used to heat homes and run automobiles (octane, as in gasoline, is C8H18)

27. Combustion Reactions Edgar Allen Poe’s drooping eyes and mouth are potential signs of CO poisoning.

28. Combustion • Example • C5H12 + O2 CO2 + H2O • Write the products and balance the following combustion reaction: • C10H22 + O2  5 6 8

29. Mixed Practice • State the type, predict the products, and balance the following reactions: • BaCl2 + H2SO4 • C6H12 + O2  • Zn + CuSO4  • Cs + Br2  • FeCO3 

30. 6.2 Factors Affecting the Rate of Chemical Reactions • Glow Sticks and Temperature • HCl and Concentration • Flour and Surface Area • Potassium Iodide and Catalysts • Diamonds and Pressure

31. Glow Sticks A temperature demonstration

32. Single replacement reaction between Mg and HCl A concentration demonstration

33. Flour Special Effects A surface area demonstration

34. Elephant Toothpaste! A catalyst demonstration – adapted using yeast catalyst

35. How does the elephant toothpaste work? • Foam is awesome! Each tiny foam bubble is filled with oxygen. • The yeast acted as a catalyst to remove the oxygen from the hydrogen peroxide. Since it did this very fast, it created lots and lots of bubbles. • The bottle got warm. The experiment created a reaction called an Exothermic Reaction - that means it not only created foam, it created energy in the form of heat! • The foam produced is just water, soap, and oxygen so you can clean it up with a sponge and pour any extra liquid left in the bottle down the drain. • This experiment is sometimes called "Elephant's Toothpaste" because it looks like toothpaste coming out of a tube, but don't get the foam in your mouth!

36. COLLISION MODEL States that the rate of reaction is affected by the number of collisions of reactant molecules. Molecules in a gas or a liquid are constantly colliding with each other.

37. EXOTHERMIC: Needs a little energy to get started Energy released overall ENDOTHERMIC: Lots of energy to get it started Energy absorbed overall

38. 5 FACTORS There are four factors that affect the rate of reaction that we will discuss. • TEMPERATURE • CONCENTRATION • SURFACE AREA • CATALYSTS • The 5th factor we will not discuss in this course. PRESSURE

39. TEMPERATURE Higher temperatures increase the rate of a chemical reaction because particles move faster at high temperatures and this creates more violent collisions more often.

40. Reaction Rate: Effect of Temperature • Activation Energy • Arrhenius: molecules must posses a minimum amount of energy to react. • In order to form products, bonds must be broken in the reactants. • Bond breakage requires energy. • Activation energy, Ea,is the minimum energy required to initiate a chemical reaction.

41. Temperature and Rate Activation Energy

42. Effect of temperature on rate Increasing temperature increases the rate

43. Effect of temperature on rate 1 Time Conclusion ? RATE Rate increases with increasing temperature TEMPERATURE

44. CONCENTRATION Higher concentration increase the rate of a chemical reaction because there are more particles to collide with.

45. Effect of concentration on rate 1 Time Conclusion ? RATE Rate is directly proportional to concentration CONCENTRATION

46. SURFACE AREA A larger surface area increases the rate of a chemical reaction because there are more exposed particles in the compound.

47. CATALYSTS A substance that increases a chemical reaction but does not get consumed by the reaction. Therefore it is not considered a reactant or product. Works by reducing the energy needed to break bonds, provides easier paths for reactions. *lowers the Ae!

49. QUESTION Explain how you would use your knowledge of factors that affect the rate of reaction to cook a steak as quickly as possible. • Temperature – increase to high • Surface Area – Cut steak into pieces (increase area) • Concentration – none • Cataylsts - none

50. QUESTION What effect on the rate of reaction of a metal with 20 ml of dilute acid at room temperature would you expect if: A) the acid was cooled to 100C? B) 2 ml of concentrated acid was added? C) the metal was ground into powder before addition to the acid?