1. Chemical Reactions Notes

2. 1. Chemical Reactions

3. A. Evidence of Chemical Reactions Four indicators a chemical reaction has occurred: –Color change –Becomes cloudy = Precipitate forms –Bubbles = Gas forms –Heat is produced (hot/light) or absorbed (cold)

4. B. Chemical Equations A chemical equation represents a chemical reaction – –Chemicals present before the reaction are shown to the left of the arrow and are called the REACTANTS. –Chemical formed by the reaction are shown to the right of the arrow and are called the PRODUCTS.

5. REACTANTS  * PRODUCTS * arrow – indicates direction of change and is read as “yields” or “produces” Example - CH 4 + 2O 2  CO 2 + 2H 2 O ReactantsYieldProducts

6. C. Reaction Rates Reaction rate depends on the collisions between reacting particles. Successful collisions occur if the particles... – with each other –have the correct –have enough to break bondsbreak bonds collide orientation kinetic energy

7. To speed up the rate of the reaction: –Increase (smaller particles or dissolve in water) –Increase (add more reactant) –Increase (add heat source) –Add surface area concentration temperature catalyze/enzyme

8. Exothermic reactions release heat –Heat is a product –Feels hot Endothermic reactions absorb heat –Heat is a reactant –Feels cold D. Heat in Reactions

9. 2. Types of Reactions Double Displacement: Single Displacement: Decomposition: Synthesis: Combustion: AB  A + B AB +YZ  AZ + YB A +YB  Y + AB A + B  AB C x H x + O 2  CO 2 + H 2 O Reactants are: 2 compounds Reactants are: 1 element & 1 Compound Reactant is: 1 compound Reactants are: 2 elements or 2 oxides Reactants are: hydrocarbon and oxygen

10. Double Displacement reactions Double Displacement reactions where the driving force is formation of a solid. Precipitation Reaction: Double Displacement reactions where the driving force is formation of a solid. Double Displacement reactions where the driving force is formation of a liquid. (water) Acid-Base/ Neutralization Reaction: Double Displacement reactions where the driving force is formation of a liquid. (water)

11. Oxidation Reduction reactions: (redox) Driving Force = Transfer of electron Always in single displacement reactions Sometimes in Synthesis and Decomposition Never in Double Displacement Example: Anytime a single element is present a reaction is also classified as redox NaCl (aq) +Na (s)  Cl 2(g) 22 NaCl (aq) +Na (s)  Cl 2(g) 22 Zn(NO 3 ) 2(aq) + 2 Na (s)  2NaNO 3(aq) + Zn (s) decomposition & redox synthesis & redox single displacement & redox

12. Learning Check Classify the following reactions: 2 KNO 3  2 KNO 2 + O 2 2 C 2 H 2 + 5 O 2  4 CO 2 + 2 H 2 O CaO + H 2 SO 4  CaSO 4 + H 2 O 3 CaCl 2 + 2 Na 3 PO 4  Ca 3 (PO 4 ) 2(s) + 6 NaCl 2 Fe + 6 HC 2 H 3 O 2  2 Fe(C 2 H 3 O 2 ) 3 + 3 H 2 2 KCl + 3 O 2  2 KClO 3

13. The reactants and the products contain the same atoms, but the chemical reaction has changed the way they are grouped. In a chemical reaction, atoms are neither created nor destroyed, all atoms present in the reactants must be present in some form in the products. Balancing an equation makes sure that there is the same number and type of atom on both sides of the equation. Law of Conservation of Mass 3. Balancing Chemical Equations

14. The chemical equation for a reaction provides us with three important pieces of information: 1.Identities of the reactants and products 2.Relative numbers of each atom 3.State of each reactant and product States of matter are shown with the following symbols: (s) solid (l) liquid (g) gas (aq) aqueous, dissolved in water

15. HINTS : –Don’t forget the diatomics – BrINClHOF if they appear by themselves they must be written as: Br 2, I 2, N 2, Cl 2, H 2, O 2, F 2, –Balance oxygen and hydrogen last. –If you have a split element, make the odd number even –If you have a polyatomic ion that does not change, balance it as the ion

16. Examples – 1.Liquid ethanol, C 2 H 5 OH, reacts with oxygen gas to produce carbon dioxide gas and water vapor. 2.Solid potassium reacts with liquid water to form hydrogen gas and potassium hydroxide that dissolves in water.

17. Examples: 1)C 3 H 8(g) + O 2(g)  CO 2(g) + H 2 O (g) 2)NH 4 NO 2(s)  N 2(g) + H 2 O (g) 3) NO (g)  N 2 O (g) + NO 2(g)

18. LEARNING CHECK: HNO 3(aq)  NO 2(g) + H 2 O (l) + O 2(g) Mg (s) + H 2 O (l)  Mg(OH) 2(s) + H 2(g)

19. 1. Soluble solid – readily dissolves in water 2. Insoluble and slightly soluble solid – a solid where such a tiny amount dissolves in water that it is undetectable to the naked eye 3. Solubility is temperature dependent State is aqueous - (aq) State is solid - (s) 4. States of Substances States of reactants can be manipulated

20. Solubility Rules (on snoopy sheet) Ex. Predict whether the following substances are soluble or insoluble. AgNO 3 Al(OH) 3 Cu 3 PO 4 Li 2 CO 3 ZnSO 4 (aq) (s) Solubility Rules Mainly water soluble (aq) All nitrates are soluble. All acetates are soluble. All chlorates are soluble. All chlorides are soluble except AgCl, Hg 2 Cl 2, and PbCl 2 All bromides are soluble except AgBr, Hg 2 Br 2, PbBr 2, and HgBr 2 All iodides are soluble except AgI, Hg 2 I 2, PbI 2, and HgI 2 All sulfates are soluble except CaSO 4, SrSO 4, BaSO 4, PbSO 4, Hg 2 SO 4, and Ag 2 SO 4 Mainly water insoluble (s) All sulfides are insoluble except those of 1A and 2A elements and (NH 4 ) 2 S All carbonates are insoluble except those of 1A and (NH 4 ) 2 CO 3 All phosphates are insoluble except those of 1A and (NH 4 ) 3 PO 4 All hydroxides are insoluble except those of 1A, Ba(OH) 2, Sr(OH) 2 and Ca(OH) 2

21. Learning Check Try these: Determine if the following are AQUEOUS or SOLID 1. lead (II) nitrate 2. potassium sulfide 3. barium hydroxide 4. ammonium carbonate Turn to your neighbor and compare answers

22. When a soluble ionic salt dissolves in water the ions separate and a hydration shell is formed around each ion (Dissociation) Ex. Ba(NO 3 ) 2 in water – Ba(NO 3 ) 2 (aq)  Ba +2 (aq) + 2 NO 3 -1 (aq) Al 2 (CO 3 ) 3 (s)  Al 2 (CO 3 ) 3 (s) or No RXN Aluminum carbonate

23. Draw a beaker of dissociated sodium chloride; a beaker of dissociated Aluminum nitrate; and a beaker of silver chloride. Na + 1 Cl -1 Na +1 Cl -1 Na +1 = sodium ion = chloride ion Al +3 NO 3 -1 Al +3 NO 3 -1 = aluminum ion = nitrate ion Cl -1 Ag +1 Cl -1 Ag +1 Cl -1 Ag +1 = silver ion = chloride ion

24. Special Rules 1. Acids are aqueous 2. Most metal oxides are solids 3. Most non-metal oxides are gases

25. Learning Check Determine the state: 1. lead(II) phosphate 2. magnesium oxide 3. nickel 4. dinitrogen monoxide 5. chlorine 6. sulfuric acid 7. sodium sulfide

26. 5. Predicting Whether a Reaction Will Occur A. Four Driving Forces 1.Formation of a solid (precipitate) 2.Formation of water 3.Transfer of electrons 4.Formation of a gas B. If a driving force occurs the reaction will take place.

27. Steps for Predicting Products 1.Formulas for reactants 2.Type of Reaction 3.Predict Product formulas (using ions) 4.States (using solubility rules) 5.Balance Equation or NO REACTION (if missing driving force) 6. Predicting Products

28. A.Double Displacement reactions: two compounds combine to produce two different compounds - Acid-Base and Precipitation Reactions. * Use solubility rules. General Equation: Example: AB + YZ  AZ + YB Lead (II) acetate + sodium chloride Pb(C 2 H 3 O 2 ) 2 (aq) + NaCl  PbCl 2 (s) + NaC 2 H 3 O 2 (aq) 22 Driving force = liquid Driving force = solid Pb +2 C 2 H 3 O 2 -1 Na +1 Cl -1

29. B. Single Replacement Reactions: Activity Series Single Displacement reactions: an element and a compound combine to form a new element and compound. **Use the activity series** General Equation: Example: A + YB  Y + AB (Cation)B + AZ  Z + AB (Anion) Sodium + Lead (II) acetate Na +1 Pb +2 C 2 H 3 O 2 -1 Na (s) + Pb(C 2 H 3 O 2 ) 2(aq)  Pb (s) + NaC 2 H 3 O 2 (aq) 22 *If you don’t know the charge use +2

30. Activity Series Active metal elements can replace less active metals, active nonmetal elements can replace less active nonmetals. Use the Activity series (snoopy sheet) to determine whether or not the reaction will occur. Driving force is the transfer of electrons.

31. 1.___ I 2 + ___ NaCl  2. ___ H 2 SO 4 + ___ NaOH  Learning Check

32. 7. Rules for Oxidation Numbers 1. The oxidation number of any uncombined element is 0. 2. The oxidation number of a monatomic ion equals the charge on the ion. 3. The more-electronegative element in a binary compound is assigned the number equal to the charge it would have if it were an ion. 4. The oxidation number of fluorine in a compound is always -1. 5. Oxygen has an oxidation number of -2 unless it is combined with F (when it is +2), or it is in a peroxide (such as H 2 O 2 or Na 2 O 2 ), when it is -1. 6. The oxidation state of hydrogen in most of its compounds is +1 unless it is combined with a metal, in which case it is -1.

33. Oxidation vs. Reduction The sum of the oxidation states in a neutral compound must equal zero and must be equal to the overall charge in an ionic compound. Assign oxidation states to each of the atoms in the following compounds: a. FeF 2 b. H 2 O c. KMnO 4 d. C 2 H 6 e. I Cl 5 f. SO 4 2- 2(-1)1(+2)1(-2)2(+1)4(-2)1(+1)+7 6(+1)2(-3)5(-1)+54(-2) +2+6 Fe = + 2, F = - 1 C = - 3, H = + 1 H = + 1, O = - 2 K = + 1, Mn = + 7, O = - 2 I = + 5, Cl = - 1 S = + 6, O = - 2 Assign oxidation states to each atom in the equation. Fe 2 O 3 + 2 Al  Al 2 O 3 + 2 Fe 0 0-2+3 -2+3 Fe gains electrons. It has been REDUCED Al lost electrons. It has been OXIDIZED

34. Remember LEO GER:LOSE ELECTRONS OXIDATION GAIN ELECTRONS REDUCTION Something that is reduced is called an oxidizing agent. Something that is oxidized is called a reducing agent. For each reaction, identify the atoms that undergo reduction, or oxidation. a.2 H 2 (g) + O 2 (g)  2 H 2 O (g) b.Zn (s) + Cu 2+ (aq)  Zn 2+ (aq) + Cu (s) c.2 AgCl (s) + H 2 (g)  2 H + (aq) + 2 Ag (s) + 2 Cl - (aq) d. 2 MnO 4 - (aq) + 16 H + (aq) + 5 C 2 O 4 2- (aq)  2 Mn 2+ (aq) + 10 CO 2(g) + 8 H 2 O (l) 00-2+1 0+2 0 +10 0 -2 +7 +1 -2 +3 +2 -2+4 -2 +1 oxidized: hydrogen (0 to +1) reduced: oxygen (0 to -2) oxidized: zinc (0 to +2) reduced: copper (+2 to 0) oxidized: hydrogen (0 to +1) reduced: silver (+1 to 0) oxidized: carbon (+3 to +4) reduced: manganese (+7 to +2)

35. Learning Check Assign oxidation states to each of the atoms in the following compounds: a. SO 2 b. S c. SO 3 Assign oxidation states to each atom in the equation. Determine which element was oxidized and which was reduced. 2 Al + 3 CuCl 2  2 AlCl 3 + 3 Cu