1 Chapter 9 (Glencoe Chemistry) “Chemical Reactions”

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

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

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

5 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

6 - Page 321 Reactants Products

7 Chemical reactions 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”

8 Symbols in equations? – Text page 323 l → the arrow separates reactants from products (arrow points to products) Use when you read “reacts to form” or yields l + sign = “and” or “reacts with” (s) = solid: Fe (s) (g) = gas:CO 2(g) l (l) = liquid: H 2 O (l) l (aq) = dissolved in water, an aqueous solution: NaCl (aq)

9 Symbols used in equations (FYI-don’t copy)  used after a product indicates a gas has been produced: H 2 ↑  used after a product indicates a solid has been produced: PbI 2 ↓

10 Symbols used in equations (FYI-don’t copy) ■ 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)

11 What is a catalyst? FYI – don’t copy 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.

12 Three Types of Equations: #1. The Word Equation l Ex: Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas. l Word Equation: Iron (III) sulfide + HCl  iron (III) chloride + hydrogen sulfide

13 Three Types of Equations: #2. 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 Write a skeleton equation for: Ex: Solid iron (III) sulfide reacts with gaseous hydrogen chloride to form iron (III) chloride and hydrogen sulfide gas. Fe 2 S 3 (s) + HCl(g)  FeCl 3 + H 2 S(g)

15 Now, read these equations: Fe (s) + O 2(g)  Fe 2 O 3(s) Cu (s) + AgNO 3(aq)  Ag (s) + Cu(NO 3 ) 2(aq) NO 2(g) N 2(g) + O 2(g)

16 Three Types of Equations #3. 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.

17 Rules for balancing: 1)Write correct formulas for all the reactants and products, using “+” and “→” 2)Count atoms 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! 4)Double-Check to make sure it is balanced & lowest ratio!

18 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. Ex: 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.

19 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

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

21 Section 11.2 Types of Chemical Reactions l OBJECTIVES: –Predict the products of the five general types of reactions.

22 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 For some, we will be able to: c) predict whether or not they will happen at all. l How? We recognize them by their reactants

23 #1 - Combination Reactions (On Foldable) 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)

24 Complete and balance: Ca + Cl 2  Fe + O 2  (assume iron (II) oxide is the product) Al + O 2  l Remember that the first step is to write the correct formulas – you can still change the subscripts at this point, but not later while balancing! l Then balance by changing just the coefficients only

25 #1 – Combination Reactions (Don’t Copy) l Additional Important Notes: a) Some nonmetal oxides react with water to produce an acid: SO 2 + H 2 O  H 2 SO 3 b) Some metallic oxides react with water to produce a base: CaO + H 2 O  Ca(OH) 2 (This is what happens to make “acid rain”)

26 #2 - Decomposition Reactions Only Copy* 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

27 #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

28 #2 - Decomposition Reactions (Don’t Copy) 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

29 #3 - Single Replacement Reactions-Don’t Copy 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)

30 #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 

31 #3 Single Replacement Reactions copy to foldable l We can even tell whether or not a single replacement reaction will happen: –Because some chemicals are more “active” than others –More active replaces less active l There is a list on page called the Activity Series of Metals* copy l Higher on the list replaces those lower.

32 The “Activity Series” of Metals Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold 1)Metals can replace other metals, provided they are above the metal they are trying to replace (for example, zinc will replace lead) 2)Metals above hydrogen can replace hydrogen in acids. 3)Metals from sodium upward can replace hydrogen in water. Higher activity Lower activity

33 The “Activity Series” of Halogens Fluorine Chlorine Bromine Iodine Halogens can replace other halogens in compounds, provided they are above the halogen they are trying to replace. 2NaCl (s) + F 2(g)  2NaF (s) + Cl 2(g) MgCl 2(s) + Br 2(g)  ??? No Reaction! ??? Higher Activity Lower Activity

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

35 #4 - Double Replacement Reactions-Don’t Copy 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 #4 - Double Replacement Reactions l Have certain “driving forces”, or reasons –Will only happen if one of the products: a) doesn’t dissolve in water and forms a solid (a “precipitate”), or b) is a gas that bubbles out, or c) is a molecular compound (which will usually be water). NOTE: pull out your Ionic Cpds Lab

37 Complete and balance: l assume all of the following reactions actually take place: CaCl 2 + NaOH  CuCl 2 + K 2 S  KOH + Fe(NO 3 ) 3  (NH 4 ) 2 SO 4 + BaF 2 

38 How to recognize which type? l Look at the reactants: E + E =Combination C =Decomposition E + C =Single replacement C + C =Double replacement

39 Practice Examples: 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 

40 #5 – Combustion Reactions-Don’t Copy 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.

41 Combustion Reaction Examples: C 4 H 10 + O 2  (assume complete) C 4 H 10 + O 2  (incomplete) C 6 H 12 O 6 + O 2  (complete) C 8 H 8 + O 2  (incomplete)

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 Reactions l Come in 5 major types. l We can tell what type they are by looking at the reactants. l Single Replacement happens based on the Activity Series l Double Replacement happens if one product is: 1) a precipitate (an insoluble solid), 2) water (a molecular compound), or 3) a gas.

44 l There are some more practice problems of balancing equations located from: l my website l Interesting Links l Balancing Equations

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46 Section 11.3 Reactions in Aqueous Solution l OBJECTIVES: –Describe the information found in a net ionic equation.

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

48 Net Ionic Equations l Many reactions occur in water- that is, in aqueous solution l When dissolved in water, many ionic compounds “dissociate”, or separate, into cations and anions l Now we are ready to write an ionic equation

49 Net Ionic Equations l Example (needs to be a double replacement reaction) AgNO 3 + NaCl  AgCl + NaNO 3 1. this is the full balanced equation 2. next, write it as an ionic equation by splitting the compounds into their ions: Ag 1+ + NO Na 1+ + Cl 1-  AgCl + Na 1+ + NO 3 1- Note that the AgCl did not ionize, because it is a “precipitate”

50 Net Ionic Equations 3. simplify by crossing out ions not directly involved (called spectator ions) Ag 1+ + Cl 1-  AgCl This is called the net ionic equation Let’s talk about precipitates before we do some other examples

51 Predicting the Precipitate l Insoluble salt = a precipitate [note Figure 11.11, p.342 (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 332 d)Your periodic table handout

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