1. 1 Chapter 11 “Chemical Reactions” Chemistry

2. 2 Bellringer #15 (Mar 9 th, 2011) l Using the information from section 11.1: –What do you call the elements/compounds on the left side of a chemical equation? –What do you call the elements/compounds on the right side of a chemical equation?

3. 3 Agenda (Mar 9 th, 2011) l Bellringer #15 l Homework Collection/Check l Write 11.1 Objectives l Begin 11.1: Writing Skeleton Equations l Homework: #2 (pg.324); Section Assessment #7-11 (don’t balance #11 yet)

4. 4 Section 11.1 Describing Chemical Reactions l OBJECTIVES: –Describe how to write a word equation.

5. 5 Section 11.1 Describing Chemical Reactions l OBJECTIVES: –Describe how to write a skeleton equation.

6. 6 Section 11.1 Describing Chemical Reactions l OBJECTIVES: –Describe the steps for writing a balanced chemical equation.

7. 7 All chemical reactions… l have two parts: 1.Reactants = the substances you start with 2.Products = the substances you end up with l The reactants will turn into the products. Reactants  Products

8. 8 - Page 321 Reactants Products

9. 9 In a chemical reaction l Atoms aren’t created or destroyed (according to the Law of Conservation of Mass) l A reaction can be described several ways: #1. In a sentence every item is a word Copper reacts with chlorine to form copper (II) chloride. #2. In a word equation some symbols used Copper + chlorine  copper (II) chloride

10. 10 Symbols in equations l the arrow (→) separates the reactants from the products (arrow points to products) –Read as: “reacts to form” or yields l The plus sign = “and” l (s) after the formula = solid: Fe (s) l (g) after the formula = gas: CO 2(g) l (l) after the formula = liquid: H 2 O (l) l (aq) after the formula = dissolved in water, an aqueous solution: NaCl (aq) is a salt water solution

11. 11 Symbols used in equations ■ double arrow indicates a reversible reaction (more later) ■ shows that heat is supplied to the reaction ■ is used to indicate a catalyst is supplied (in this case, platinum is the catalyst)

12. 12 What is a catalyst? l A substance that speeds up a reaction, without being changed or used up by the reaction. l Enzymes are biological or protein catalysts in your body. (what do enzymes in our body speed up?)

13. 13 #3. The Skeleton Equation l Uses formulas and symbols to describe a reaction –but doesn’t indicate how many; this means they are NOT balanced l All chemical equations are a description of the reaction.

14. 14 Write a skeleton equation for: 1. Acetylene (C 2 H 2 ) reacts with oxygen to produce carbon dioxide and water. 2. Heated mercury (II) oxide reacts to form mercury and oxygen. 3. Hydrochloric acid reacts with zinc to produce aqueous zinc chloride and hydrogen gas. 4. Acetylene gas (C 2 H 2 ) burns in a welding torch with oxygen to form carbon dioxide gas and water vapor.

15. 15 Write a skeleton equation for: 1. Solid iron (III) sulfide reacts with gaseous hydrogen chloride (HCl) to form iron (III) chloride and hydrogen sulfide gas (H 2 S). 2. Nitric acid (HNO 3 ) dissolved in water reacts with solid sodium carbonate (Na 2 CO 3 )to form liquid water and carbon dioxide gas and sodium nitrate (NaNO 3 ) dissolved in water.

16. 16 Bellringer #16 (Mar 10 th, 2011) l Hydrogen gas and oxygen gas react to form water vapor. –Write the SKELETON equation for the statement above

17. 17 Agenda (Mar 10 th, 2011) l Bellringer #16 l Homework Check l Learn how to BALANCE chemical equations l Hmwk: #1-10 on Balancing Equations Wkst; Cornell Notes 11.2

18. 18 #4. Balanced Chemical Equations l Atoms can’t be created or destroyed in an ordinary reaction: –All the atoms we start with we must end up with (meaning: balanced!) l A balanced equation has the same number of each element on both sides of the equation.

19. 19 Rules for balancing: 1)Assemble the correct formulas for all the reactants and products, using “+” and “→” 2)Count the number of atoms of each type appearing on both sides 3)Balance the elements one at a time by adding coefficients (the numbers in front) where you need more - save balancing the H and O until LAST! (hint: I prefer to save O until the very last) 4)Double-Check to make sure it is balanced.

20. 20 l Never change a subscript to balance an equation (You can only change coefficients) –If you change the subscript (formula) you are describing a different chemical. –H 2 O is a different compound than H 2 O 2 l Never put a coefficient in the middle of a formula; they must go only in the front 2 NaCl is okay, but Na 2 Cl is not.

21. 21 Practice Balancing Examples _AgNO 3 + _Cu  _Cu(NO 3 ) 2 + _Ag _Mg + _N 2  _Mg 3 N 2 _P + _O 2  _P 4 O 10 _Na + _H 2 O  _H 2 + _NaOH _CH 4 + _O 2  _CO 2 + _H 2 O 2 2 3 4 5 22 2 22

22. 22 Bellringer #18 (Mar 14 th, 2011) l Based on your 11.2 Cornell Notes: –What are the five MAIN types of chemical reactions?

23. 23 Agenda (Mar 14 th, 2011) l Bellringer #18 l Homework Collection l Write 11.2 Objectives l Review 11.2 l Exit Slip 11.2 l Homework: pg. 339 #22-25 and pg.347 #52 l Quiz Tomorrow

24. 24 Section 11.2 Types of Chemical Reactions l OBJECTIVES: –Describe the five general types of reactions.

25. 25 Section 11.2 Types of Chemical Reactions l OBJECTIVES: –Predict the products for combination and decomposition reactions.

26. 26 Types of Reactions l There are probably millions of reactions. l We can’t remember them all, but luckily they will fall into several categories. l We will learn: a) the 5 major types. l We will be able to: b) predict the products. l How? We recognize them by their reactants

27. 27 #1 - Combination Reactions l Combine = put together l 2 substances combine to make one compound (also called “synthesis”) Ca + O 2  CaO SO 3 + H 2 O  H 2 SO 4 l We can predict the products, especially if the reactants are two elements. Mg + N 2  Mg 3 N 2 (symbols, charges, cross)

28. 28 Complete and balance: Ca + Cl 2  Al + O 2  l Step 1: write the correct formulas – you can ONLY change the subscripts at this point, but not later while balancing! l Then balance by changing just the coefficients only

29. 29 #2 - Decomposition Reactions l decompose = fall apart l one reactant breaks apart into two or more elements or compounds. l NaCl Na + Cl 2 l CaCO 3 CaO + CO 2 l Note that energy (heat, sunlight, electricity, etc.) is usually required

30. 30 #2 - Decomposition Reactions l We can predict the products if it is a binary compound (which means it is made up of only two elements) –It breaks apart into the elements: lH2OlH2O l HgO

31. 31 #2 - Decomposition Reactions l If the compound has more than two elements you must be given one of the products –The other product will be from the missing pieces l NiCO 3 CO 2 + ___ H 2 CO 3 (aq)  CO 2 + ___ heat

32. 32 #3 - Single Replacement Reactions l One element replaces another l Reactants must be an element and a compound. l Products will be a different element and a different compound. Na + KCl  K + NaCl F 2 + LiCl  LiF + Cl 2 (Cations switched) (Anions switched)

33. 33 #3 Single Replacement Reactions l Metals will replace other metals (and they can also replace hydrogen) K + AlN  Zn + HCl  l Think of water as: HOH –Metals replace the first H, and then combines with the hydroxide (OH). Na + HOH 

34. 34 #3 Single Replacement Reactions Practice: Fe + CuSO 4  Pb + KCl 

35. 35 #4 - Double Replacement Reactions l Two things replace each other. –Reactants must be two ionic compounds, in aqueous solution NaOH + FeCl 3  –The positive ions change place. NaOH + FeCl 3  Fe +3 OH - + Na +1 Cl -1 = NaOH + FeCl 3  Fe(OH) 3 + NaCl

36. 36 Complete and balance: l assume all of the following reactions actually take place: CaCl 2 + NaOH  KOH + Fe(NO 3 ) 3 

37. 37 How to recognize which type? l Look at the reactants: (E = element and C = Compound) E + E =Combination C =Decomposition E + C =Single replacement C + C =Double replacement

38. 38 Name the type of reaction: H 2 + O 2  H 2 O  Zn + H 2 SO 4  HgO  KBr + Cl 2  AgNO 3 + NaCl  Mg(OH) 2 + H 2 SO 3 

39. 39 #5 – Combustion Reactions l Combustion means “add oxygen” l Normally, a compound composed of only C, H, (and maybe O) is reacted with oxygen – usually called “burning” l If the combustion is complete, the products will be CO 2 and H 2 O. l If the combustion is incomplete, the products will be CO (or possibly just C) and H 2 O.

40. 40 Combustion Reaction Examples: C 4 H 10 + O 2  CO 2 + H 2 O (complete) C 4 H 10 + O 2  CO + H 2 O (incomplete) C 6 H 12 O 6 + O 2  CO 2 + H 2 O (complete) C 8 H 8 + O 2  CO + H 2 O (incomplete)

41. 41 Type of ReactionDefinition  Equation Combination Decomposition Single Replacement Double Replacement Combustion When oxygen reacts with a element or compound to produce H 2 O and CO 2 (complete) or CO (incomplete) C x H y + O 2 → CO 2 + H 2 O A = Red B = Blue C = Green D = Yellow A + B → AB AB → A + B AB + C → AC + B AB + CD → AC + BD Two or more elements or compounds combine to make a more complex substance Compounds break down into simpler substances Occurs when one element replaces another one in a compound Occurs when different atoms in two different compounds trade places

42. 42 SUMMARY: An equation... l Describes a reaction l Must be balanced in order to follow the Law of Conservation of Mass l Can only be balanced by changing the coefficients. l Has special symbols to indicate the physical state, if a catalyst or energy is required, etc.

43. 43 Exit Slip 11.2 1) P + O 2 → P 4 O 10 5) Mg + O 2 → MgO 2) HgO → Hg + O 2 6)Al 2 O 3 → Al + O 2 3) Cl 2 + NaBr → NaCl + Br 2 7) H 2 + N 2 → NH 3 4) BaCl 2 + Na 2 SO 4 → NaCl + BaSO 4 8)CuCl 2 + H 2 S → CuS + HCl Identify the reactions below as COMBINAITON, DECOMPOSITION, SINGLE REPLACEMENT, or DOUBLE REPLACEMENT. Use the symbols below INSTEAD of writing the entire word. C = Combination D = Decomposition SR = Single Replacement DR = Double Replacement

44. 44 Agenda (Mar 16 th, 2011) l Bellringer: Copy chart on loose leaf l Check 11.3 Cornell Notes l Write 11.3 Objective l Review 11.3: How to Predict Formation of a Precipitate l Class Demo: Fill out chart based on demo l Hmwk: pg.344 #31,34, 35

45. 45 Section 11.3 Reactions in Aqueous Solution l OBJECTIVES: –Predict the formation of a precipitate in a double replacement reaction.

46. 46 Predicting the Precipitate l Insoluble salt = a precipitate [note Figure 11.3, p.344 (AgCl)] l General solubility rules are found: a)Table 11.3, p. 344 in textbook b)Reference section - page R54 (back of textbook) c)Lab manual Table A.3, page 33

47. 47 Formation of a Precipitate

48. 48 Solubility Rules (pg. 344) CompoundsSolubility Salts of alkali metals and ammonia Soluble (no precipitate) Nitrate salts and chlorate saltsSoluble (no precipitate) Sulfate salts except compounds with Pb2+, Ag+, Hg2+, Ba2+, Sr2+, and Ca2+ Soluble (no precipitate) Chloride salts except compounds with Ag+, Pb2+, and Hg2+ Soluble (no precipitate) Carbonates, phosphates, chromates, sulfides, and hydroxides Most are insoluble (precipitate)

49. 49 Bellringer #20 (March 18 th, 2011) l Predict the products the reactants below will form for the following reactions: –Mg + HCl –Fe + O 2 (Fe-iron has a 4+ charge) –H 2 O

50. 50 Agenda (March 18 th, 2011)

51. 51 Let’s do some examples together of net ionic equations, starting with these reactants: BaCl 2 + AgNO 3 → NaCl + Ba(NO 3 ) 2 →