1. Chemical Reactions and Equations Chapter 6

2. Objectives 6.1 Relate chemical changes and macroscopic properties. 6.1 Demonstrate how chemical equations describe chemical reactions 6.1 Illustrate how to balance chemical reactions by changing coefficients

3. Objectives 6.2 Distinguish among the five major types of chemical reactions 6.2 Classify a reaction as belonging to one of five major types 6.2 Predict the products of chemical reactions

4. Balancing Chemical Equations CH 4 (g) + O 2 (g)  CO 2 (g) + H 2 O (l) – Reactants  Products Coefficients. Change these to change how many of the molecule you want – CH 4 + 2 O 2  CO 2 + 2 H 2 O Do not change the subscripts, the molecule is what it is – CH 4 + 2 O 2  CO 2 + 2 H 2 O

5. States of Matter CH 4 (g) + O 2 (g)  CO 2 (g) + H 2 O (l) (g) = Gas (l) = Liquid (pure) (s) = Solid (aq) = Aqueous (Dissolved in water)

6. Balance by Guess and Check Keep track of number of atoms on each side H 2 + N 2  NH 3 ReactantsProducts – 2 H3 H – 2 N1 N Change coefficient and count again

7. Energy Endothermic: Energy is a reactant – In later courses (or this year ) we will discuss the actual numbers Exothermic: Energy is a product – Mg + O  MgO + Energy (Heat)

8. Evidence of Chemical Change – Four Evidences Change in energy (heat/cold/light) Change in color Precipitate formed (solid) Gas formed (but not due to heat)

9. Types of Chemical Reactions 5 chemical reactions – Synthesis – Decomposition – Single Displacement – Double Displacement – Combustion 38

10. Types: Synthesis Example C + O 2 OO C +  OO C OO C OO C O O C O O C O O C O O C O O C O O C O O C O O C O O C O O C O O C O O C General: A + B  AB

11. Types: Decomposition Example: NaCl General: AB  A + B  Cl Na Cl + Na

12. Types: Decomposition Example 2HgO  O Hg O OO + General: AB  A + B

13. Types: Single displacement Example: Zn + CuCl 2  Zn Cl Cu + General: AB + C  AC + B Cl Zn Cu +

14. Types: Double displacement Example: MgO + CaS General:AB + CD  AD + CB S O  Mg Ca + O S Mg Ca +

15. The 5 reactions you must know (for now) combustion: AB + oxygen  oxides of A & B synthesis: A + B  C decomposition: AB  A + B single displacement: A + BC  AC + B double displacement: AB + CD  AD + CB

16. a)Mg + HCl  MgCl 2 + H 2 b) Ca + N 2  Ca 3 N 2 c)NH 4 NO 3  N 2 O + H 2 O d) BiCl 3 + H 2 S  Bi 2 S 3 + HCl e) C 4 H 10 + O 2  CO 2 + H 2 O f) O 2 + C 6 H 12 O 6  CO 2 + H 2 O g) NO 2 + H 2 O  HNO 3 + NO h)Cr 2 (SO 4 ) 3 + NaOH  Cr(OH) 3 + Na 2 SO 4 i)Al 4 C 3 + H 2 O  CH 4 + Al(OH) 3 What type of Reaction?

17. What type of reaction? Sodium (s) + Chlorine (g)  – Sodium Chloride (s) Calcium Carbonate (s)  – Calcium Oxide (s) + Carbon Dioxide (g) C 3 H 8 (g) + O 2  – CO 2 + H 2 O Phosphorus pentachloride (s)  – Phosphorus trichloride (s) + Chlorine (g)

18. What type of reaction? Nitrogen Monoxide (g) + Ozone (g)  – Nitrogen dioxide (g) + Oxygen (g) Chlorine (g) + Ozone (g)  – Hypochlorite (g) + Oxygen (g) Silver Nitrate (aq) + Barium Chloride (s) –  Silver Chloride (s) + Barium Nitrate (aq) Calcium Oxide (s) + water (l)  – Calcium Hydroxide (s)

19. Predict the Products NaCl + Ag react in a single displacement reaction, what is the product? – Switch the metals Potassium (K) and Oxygen react in a synthesis reaction, what is the product? – Make an ionic compound Oxygen and Methane react in a combustion reaction, what is the product? – Water and Carbon Dioxide

20. Objectives 6.3 Demonstrate factors that influence the direction of a reaction. 6.3 Classify factors that influence the rate of a reaction. 6.3 Writing Equilibrium expressions

21. Introduction Some chemical reactions are fast and some are slow Which of the below are fast and which are slow? – Rusting of Iron – Firecracker explosion – Food becoming rotten – Diamond turning into graphite

22. Factors Influencing Rate of Reaction: Temperature Temperature Increase Temp  Increase Rate – Putting food into the fridge slows down the decomposition – Cold-blooded reptiles sunbathing – General rule of Thumb: Every 10 Celsius = 2x the rate

23. Factors Influencing Rate of Reaction: Pressure Pressure Increase Pressure  Increase Rate Only for gases – Increased Pressure means increased rate of chemicals colliding with one another

24. Factors Influencing Rate of Reaction: Concentration Concentration Increase Concentration  Increase Rate – Due to more molecules per volume

25. Factors Influencing Rate of Reaction: Surface Area Surface Area Increase Surface Area  Increase Rate – Grain elevator explosions (fine powder = lots of surface area) – When starting a fire, you begin with small pieces of timber

26. Chemical Engineering – These factors are very important to chemical engineers who are responsible for producing much of the chemicals we use. – The speed and ease with which it can be made often determine the cost.

27. Chemical Equilibrium Dynamic Equilibrium

28. Major Ideas Completion reactions Reversible Reactions Dynamic Equilibrium

29. Chemical Reactions – Up until now, we have only considered reactions that only go one direction. This unit we will consider reactions that go both directions, called reversible reactions.

30. The Difference Reversible Reaction: – Reactants  Products and – Products  Reactants Completion Reaction: – Reactants  Products only

31. Completion/Reversible What does this mean? In any chemical reaction, it is a competition between two competing reactions. In a completion reaction, one side wins big. In a reversible reaction, the contest is more evenly matched.

32. Consider the following Completion reaction HCl (aq) + H 2 O (l)  H 3 O + (aq) + Cl - (aq) When a HCl and water come into contact, the H leaves the Cl and joins the water. When a Hydronium comes into contact with a Cl-, the H doesn’t come back to the Cl-.

33. Why Not? Strength of Bonds (Enthalpy) – If a chemical is produced which has a very strong bond, then the molecule will not be broken apart Increased disorder on product side (Entropy) – Haven’t discussed this yet, but chemical reactions are more likely to occur when disorder increases

34. Consider the following Reversible Reaction Ca +2 (aq) + SO 4 -2 (aq)  CaSO 4 (s) The calcium ion and sulfate ion are trying to react to make a solid. The solid is decomposing to try to make the ions. This is a reversible reaction because neither side wins all the time

35. Dynamic Equilibrium Eventually, over time, the reversible reaction will find some concentration where both sides are reacting at the same rate. Even when chemical reactions appear to have stopped, the battle rages on. – Static Equilibrium: You sit on a chair (force of gravity = force of chair on you) – Dynamic Equilibrium: Equal rate of reaction NOT necessarily equal amounts of Reactants/Products

36. Equilibrium = Equal Rates At Equilibrium, the forward and reverse reaction are occurring at the same rate When a Calcium Sulfate solution reaches equilibrium, for every Calcium and Sulfate that combine, one Solid Calcium Sulfate decomposes.

37. Reaching Equilibrium

38. Another Example

39. Completion Reaction

40. Products Favored

41. Both equally favored

42. Reactants Favored

43. Changing the direction or who is favored Add Reactants  Add Products  If endothermic, add heat (increase Temp)  If exothermic, take away heat  If gases present, increasing pressure favors side with fewer gas molecules

44. Other Related Ideas Activation Energy: The amount of energy the particles need when colliding for the atoms to rearrange Reaction Rate: Related to Activation Energy – Fast Reaction Rates generally means low activation energy – Slow Reaction Rates generally mean high activation energies

45. Other related ideas Catalyst: Speed up reaction by lowering activation energy – Participate in helping reaction, but are not changed by reaction Inhibitor: Slow down reaction Enzyme: Biological Catalyst

46. Practice Question N 2 (g) + 3 H 2 (g)  2 NH 3 (g) – How will the reaction react to … a) Addition of Nitrogen gas? b) Removal of Hydrogen gas? c) Increase in Temperature? d) Increase in Pressure? e) What are the best conditions for the production of ammonia, considering pressure and temperature?

47. Practice Question 3 Fe(s) + 4 H 2 O (g)  Fe 3 O 4 (s) + 4 H 2 (g) + heat a) Increase the amount of water b) Decrease the volume by half c) Remove Fe 3 O 4 as it is formed d) Add hydrogen to the mixture e) Increase the temperature f) Adding a catalyst

48. Non-Athlete  Athlete Hungry Student  Full Student

49. Demo – [Cu(H 2 O) 4 ] +2 (aq) + 4 Cl -1  – [CuCl 4 ] -2 (aq) + 4 H 2 O (l)