1. Chemical Reactions CHAPTER 11

2. WHAT ARE OUR REPRESENTATIVE, OR BASIC PARTICLES? They are the smallest pieces of a substance. For a molecular compound: it is the molecule. For an ionic compound: it is the formula unit (ions). For an element: it is the atom. Remember the 7 diatomic elements (made of molecules)

3.  Signs of a chemical reactions : 1.Evolution of Heat and Light (temperature change) 2. Formation of a Precipitate 3. Formation of a Gas 4. Color change  Law of Conservation of Mass: Mass can neither be created of destroyed (i.e., mass remains same), atoms are rearranged. 4 g 32 g 36 g

4. WHAT IS A CHEMICAL REACTION? A chemical reaction occurs when 1 or more compounds (elements) are reacted to produce totally new compounds that have different chemical and physical properties than they did before. A chemical reaction is represented by writing a chemical equation. Included are: 1.Chemical Formulas; H 2, H 2 O, CaCl 2, etc 2.Symbols; , (g), (aq), (s) 3.Coefficients; 1, 2, 3, etc

5. CHEMICAL EQUATION  A chemical reaction has two parts:  Reactants: Substances you start with  Products: Substances you end up with  Coefficients: are small whole numbers that are placed in front of the formulas in an equation in order to balance it. Reactants → Products

6. THE ANATOMY OF A CHEMICAL REACTION 2 H 2 + O 2  2 H 2 O “Yields” or Produces Subscript: Number of Atoms present Coefficient: how many of that molecule Reacts with Ingredients are called the “REACTANTS” Results are called the “PRODUCTS”

7. SYMBOLS USED IN CHEMICAL EQUATIONS Pt

8. CHEMICAL EQUATION Chemical Equation can be written in 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

9. 3. In a skeleton equation: uses formulas and symbols to describe a reaction Fe(s) + O 2 (g) → Fe 2 O 3 (s) H 2 O 2 (aq) H 2 O(l) + O 2 (g) MnO 2

10. BALANCING CHEMICAL EQUATIONS 3CO 2 (g)  2Mg(s)  4MgO(s)  3 molecules of carbon dioxide in gas state 2 atoms of magnesium in solid state 4 units of magnesium oxide in solid state

12. PRACTICE BALANCING EXAMPLES _Mg + _N 2  _Mg 3 N 2 _P + _O 2  _P 4 O 10 _AgNO 3 + _Cu  _Cu(NO 3 ) 2 + _Ag _CH 4 + _O 2  _CO 2 + _H 2 O 2 3 4 5 2 2 2

13. TYPES OF CHEMICAL REACTIONS By classifying chemical reactions, one can easily predict the products formed. Five general types of Reactions 

14. 1.Combination Reactions: Two substances combine to make one compound (also called “synthesis”) 2Ca(s) + O 2 (g)  CaO (s) We can predict the products, especially if the reactants are two elements. 2Mg (s) + O 2 (g)  gO   s) Ca (s) + Cl 2 (g)  CaCl 2  s  2Fe(s) + O 2 (g)  2FeO (s) 4Al (s) + 3O 2 (g)  Al 2 O 3(s)

15. 2. Decomposition Reaction : is a chemical change in which a single compound breaks down into two or more simpler products. 2Na 3 N (s) → 6Na(s) + N 2 (g) 2H 2 O(l) 2H 2 (g) + O 2 (g) 3. Single-Replacement Reactions: is a chemical change in which one element replaces a second element in a compound. electricity A + BC  AC + B

16. SINGLE REPLACEMENT REACTIONS There are generally two types of single replacement reactions Keep in mind … Na F Cationic: A metal can replace a metal A + BC  AC + B (A & B are metals) Anionic: A nonmetal can replace a nonmetal D + EF  ED + F (D & F are nonmetals) cationic metal anionic nonmetal

17. THE ACTIVITY SERIES OF THE METALS Lithium Potassium Calcium Sodium Magnesium Aluminum Zinc Chromium Iron Nickel Lead Hydrogen Bismuth Copper Mercury Silver Platinum Gold  Metals can replace other metals provided that they are above the metal that they are trying to replace  Metals above hydrogen can replace hydrogen in acids.  Metals from sodium upward can replace hydrogen in water

18. THE ACTIVITY SERIES OF THE HALOGENS Fluorine Chlorine Bromine Iodine Halogens can replace other halogens in compounds, provided that they are above the halogen that they are trying to replace. 2NaCl(s) + F 2 (g)  2NaF(s) + Cl 2 (g) MgCl 2 (s) + Br 2 (g) ???No Reaction ???

19. 4. Double-Replacement Reactions: is a chemical change involving an exchange of positive ions between two compounds. Also known as Double Displacement reactions or Metathesis reactions. AB + CD  AD + CB 2KI(aq) + Pb(NO 3 ) 2 (aq) → PbI 2 + 2KNO 3 (aq)

20. For a double-replacement reaction to occur, one of the following is usually true: 1.One of the products is only slightly soluble and precipitates from solution. 2.One of the products is a gas. 3.One product is a molecular compound such as water. K 2 CO 3 (aq) + BaCl 2 (aq) → 2KCl(aq) + BaCO 3 (s) 2NaCN(aq) + H 2 SO 4 (aq) 2HCN(g) + Na 2 SO 4 (aq) Ca(OH) 2 (aq) + 2HCl (aq) CaCl 2 (aq) + 2H 2 O (l)

21. PREDICTING THE FORMATION OF A PRECIPITATE

22. NET IONIC EQUATION Many reactions occur in water- that is, in aqueous solution When dissolved in water, many ionic compounds “dissociate”, or separate, into cations and anions Example (needs to be a double replacement reaction) AgNO 3 (aq) + NaCl(aq) → AgCl(s) + NaNO 3 (aq)

23. Need to do three steps to write net ionic equation 1. The equation should be a balanced full equation 2. Then write a complete ionic equation 3. Complete ionic equation can be simplified by eliminating ions not directly involved (spectator ions) = net ionic equation

24. 1. Full balanced equation 2. Complete Ionic Equation 3. Net Ionic Equation Spectator Ions : Na + and NO 3 - ; Ions that appear on both sides of an equation Ag + (aq) + Cl – (aq) → AgCl(s) AgNO 3 (aq) + NaCl(aq) → AgCl(s) + NaNO 3 (aq) Ag + (aq) + NO 3 – (aq) + Na + (aq) + Cl – (aq) → AgCl(s) + Na + (aq) + NO 3 – (aq)

25. 5. Combustion Reactions : is a chemical change in which an element or a compound reacts with oxygen, often producing energy in the form of heat and light. A combustion reaction always involves oxygen as a reactant. CH 4 (g) + 2O 2 (g) → CO 2 (g) + 2H 2 O(g)

26. Often the other reactant is a hydrocarbon, which is a compound composed of hydrogen and carbon. In a combustion reaction when one of the reactant is a hydrocarbon, the products are carbon dioxide and water. 2C 8 H 18 (l) + 25O 2 (g) → 16CO 2 (g) + 18H 2 O(g) 4C 25 H 53 (s) + 103O 2 (g) → 100CO 2 (g) + 106H 2 O(g)