Chemical Equations and Reactions

1. Chemical Equations andReactions Chemistry Chapter 8 2/23/09

2. Reminders!!!!!!!!! As I have said many time over the last few weeks� ASK QUESTIONS� ASK ME TO SLOW DOWN!!!! I know this stuff� You don�t� Make sure you tell me when to slow down and go over something again! Do not forget vocabulary will be due on the day of your chapter eight test!!!!!!! 9 Terms for 9points

3. What do you know? What are some signs that a chemical change may be taking place? What are the reactants of a reaction? What are the products of a reaction? Describe the law of conservation of mass. What are some types of reactions that we talked about before winter break?

4. Here�s What I Know Formation of a gas or solid, change in color or odor, and release/absorption of energy Reactants are what you start with and products are what you form Law of conservation of mass means however much mass you start with you must end with We talked about synthesis, decomposition, single and double replacement reactions

5. Check This Out! 5g of baking soda 5mL of vinegar Total mass=_______ Now I will pop the top and we will see what happens Final Total mass=________

6. Describing Chemical ReactionsSection One Goals List evidence that suggests that a chemical reaction has occurred Describe a chemical reaction by using a word equation and a formula equation Interpret notations in formula equations, such as those relating to states of matter or reaction conditions

7. Chemical Change Give me a few examples of CHEMICAL change Chemical reaction=> the process by which one or more substances change to produce one or more different substances Atoms do not become other types of atoms nor do they appear or disappear The bonding patterns among the atoms are merely rearranged

8. Reactants vs. Products Reactants are what you start with or the �original substances� Products are what you end up with or the �new substances� Example: Camp fire- reactants: wood and fire/match� products: carbon dioxide and water

9. Evidence of a Chemical Change Change in energy Release of heat Release of light Production of sound Change in temperature Change in electrical energy Formation of a new substance Formation of a gas Formation of a precipitate (solid) Change in color Change in odor

10. Chemical Reaction vs. Physical Change Only way to know for sure that an actual chemical reaction has taken place is to do a chemical analysis on the products These test would show that the new substances� density, melting point or boiling point are different then the reactants�

11. Examples Even though you have a color change when you mix paints, the final chemical composition is still the same as when you started (physical change) Copper reacting with nitric acid also has a color change, but it is a chemical change because you end up with two totally different products

12. Reactions and Energy Changes Reactions can gain or lose energy methane + oxygen -> carbon dioxide + water + energy Energy is released it is a product (exothermic) Dinitrogen tetroxide + energy -> nitrogen dioxide Energy is absorbed it is a reactant (endothermic)

13. More on Energy Changes Exothermic reactions yield stronger bonds This is because the bonds holding the products together are stronger than those in the reactants The stronger the bond the more energy released when bond forms and more energy to break more bonds in the reactants

14. One Last Thing On Energy

15. Do You Remember? For a reaction to take place the reactants actually have to� Come into contact with each other Example: the potassium chlorate on match heads must contact the phosphorus on the matchbox

16. Chemical Equation A representation of a chemical reaction that uses symbols to show the relationship between the reactants and the products Must obey the law of conservation of mass Number of atoms on each side of the arrow must be the same

17. Writing a Word Equation Follow the steps to get it right! 1) Write down the names of the reactants 2) Put a plus sign between any reactants 3) Draw an arrow to the left of the reactants 4) Write down the names of the products after the arrow 5) Place a plus sign between any products

18. Try This! Methane reacts with oxygen to form carbon dioxide and water Make this a word equation (Follow the steps!) methane + oxygen -> carbon dioxide + water

19. Writing a Formula Equation Follow these steps 1) Replace the formulas for the names in the word equation 2) Put a question mark (?) in front of each formula 3) Even out the number of atoms of each element on each side by replacing the (?) with numbers

20. Few Tips 1) Delay the balancing of elements (often H and O) that occur in several reactants or products 2) If the same polyatomic ions appear on both sides of the equation, treat them as single units, like monatomic ions 3) After using steps 1&2, balance the elements left to right 4) Remember, balancing one element may unbalance others (So ALWAYS double check at the end!!!) 5) For ionic equations, be sure charges are balanced (If/when we use these)

21. Try This One! methane + oxygen -> carbon dioxide + water Make this a formula equation ?CH4 + ?O2 -> ?CO2 + ?H2O CH4 + 2O2 -> CO2 + 2H2O

22. So� What Do All the Number Mean?

23. Important Information Chemical equations tell more than just what is used and made in a reaction Shows how much of everything is in a reaction Tells temperature and/or pressure needed for the reaction

24. Check This Out! NaHCO3(s) + HC2H3O2(aq) -> NaC2H3O2(aq) + CO2(g) + H2O(l) N2(g) + 3H2(g) 350�C, 25,000kPa 2NH3(g) catalyst Tells a little bit about each compound in the reaction

25. State Symbols and Reaction Conditions Open your book to page 265 Table 2 is a list of many symbols that you will need to know/use for writing equations

26. How About Now? List evidence that suggests that a chemical reaction has occurred Describe a chemical reaction by using a word equation and a formula equation Interpret notations in formula equations, such as those relating to states of matter or reaction conditions

27. �Balancing Chemical Equations�Section Two Goals Relate the conservation of mass to the rearrangement of atoms in a chemical reaction Write and interpret a balanced chemical equation

28. Conservation of Mass In ordinary chemical or physical changes, mass is neither created nor destroyed Think back to the demonstration I did with the baking soda and vinegar The mass of everything I started with was the same as what I ended with

29. Not Making New Atoms Remember we said that all we are doing is rearranging the atoms not making new atoms For this reason our mass does not change only the compounds we have change You can also tell this by looking at balanced equations 2Na + 2H2O -> 2NaOH + H2 The types of atoms we start with are the same types we end with

30. Balancing EquationsDo You Remember???? Number on left side of the arrow must equal the number on the right side of the arrow Hence the balance part of balanced equations We can only change the coefficients Coefficient=> a small whole number that appears as a factor in front of a formula in a chemical equation H20 compared to 2H2O 3Ca(NO3)2

31. One More Time Here�s how to do it: 1) Identify reactants and products 2) Count atoms 3) Insert coefficients 4) Check your final answer

32. Sample Problem APage 269 Balance the equation for the reaction of iron(III)oxide with hydrogen to form iron and water. 1) Identify reactants and products Fe2O3 + H2 -> Fe + H2O 2) Count atoms Make a chart 3) Insert coefficients Fe2O3 + 3H2 -> 2Fe + 3H2O 4) Check final answer Fix chart to match the coefficients you used in step 3 and make sure everything is even

33. Your Turn Try numbers 2 and 3 on page 269 Make sure to follow the steps!!!

34. Never Ever Ever!!!!! DO NOT CHANGE SUBSCRIPTS If you change these your are changing the compounds in the reactions!!! We can only change the coefficients to make the number of atoms balance When we change these we are just changing the number of moles of the substance needed in the reaction

35. �Odd-Even Technique�Sample Problem BPage 271 The reaction of ammonia with oxygen produces nitrogen monoxide and water vapor. Write the balanced equation for this reaction. 1) NH3 + O2 -> NO + H2O 2) **When using the odd-even we know that an odd number multiplied by 2 gives us an even number 3) 4NH3 + 5O2 -> 4NO + 6H2O 4) Double Check

36. Your Turn! Try numbers 2&3 of Sample Problem B page 271

37. Polyatomic Ions and Balancing Sometimes a polyatomic ion will stay intact throughout the reaction so when we go to balance the equation we can think of it as its own �atom� Example: 2Al + 3H2SO4 -> Al2(SO4)3 + 3H2

38. Sample Problem CPage 273 Aluminum reacts with arsenic acid(HAsO3), to form H2 and aluminum arsenate. Write a balanced equation for this reaction. Al + HAsO3 -> H2 + Al (AsO3)3 2Al + 6HAsO3 -> 3H2 + 2Al (AsO3)3

39. Your Turn! Try number 1&2 on page 273

40. �Classifying Chemical Reactions�Section 3Goals Identify combustion reactions, and write chemical equations that predict the products Identify synthesis reactions, and write chemical equations that predict the products Identify decomposition reactions, and write chemical equations that predict the products Identify displacement reactions and use the activity series to write chemical equations that predict the products Identify double-replacement reactions, and write chemical equations that predict the products

41. Types of Reactions We classify reactions to make predicting the products easier Each type of reaction follows a certain pattern which make balancing easier:)

42. As AlwaysThere�s a Catch The 5 reactions we talk about are not the only types Each reaction does not have to fit into just one type Maybe more than one maybe none

43. Combustion Reactions Combustion reaction=> reaction of a carbon-based compound with oxygen Products are carbon dioxide and water vapor Used to generate energy Ex: the lighting in here is because of the combustion of coal Do you have any others?

44. Hydrocarbons Just a fancy way to say the compound only has hydrogen and carbon in it Example: Propane C3H8 + 5O2 -> 3CO2 + 4H2O

45. Alcohols Made of carbon, hydrogen, and oxygen Products are still only carbon dioxide and water vapor Example: Ethanol CH3CH2OH + 3O2 -> 2CO2 + 3H2O

46. How Do We Get Soot? Anytime we have combustion reaction that does not have enough oxygen then we end up with soot (unburned carbon) and carbon We also end up with carbon dioxide and water vapor

47. Synthesis Reactions Synthesis means �to put together� so� Synthesis Reaction=> a single compound forms from two or more reactants Indicator: if you only have one product or if you only have two elements or small compounds as reactants

48. Binary Compound Composed of two elements The left side of the periodic table wants to react with the right side of the table Isn�t always easy to tell what compound will form at the end Example: Carbon and Oxygen

49. Ternary Compound Two compounds combine to form a ternary compound Compound of three elements Example: CaO + H2O -> Ca(OH)2(s)

50. Decomposition Reactions Decomposition Reaction=> a single compound breaks down into two or more elements or simpler compounds Opposite of synthesis reactions Often need an input of energy to make the reaction happen

51. Examples Often when you start with a binary compound you end up with the two elements that made up your reactant Water We use the gases from water in hospitals� very expensive because of the energy needed to make the decomposition happen

52. Cool Fact We are now trying to make solar cells that will be able to give the energy needed to break apart water

53. Sample Problem DPage 279 Predicting Products Let�s try them together!!!

54. Displacement Reactions Metals can replace metals or hydrogen Nonmetals can replace nonmetals In these reactions a single element reacts with a compound and displaces another element from the compound Like they switch places

55. Activity Series Activity series=> a series of elements that have similar properties and that are arranged in descending order of chemical activity Page 281 Table 4 �Activity Series� Appendix A has a more complete table!!!

56. More on Activity Series Elements can only �switch� places with elements below it on the activity series

57. How To� (Page 281) 1) Identify the reactants Determine if element is metal or halogen Determine the element that might be displaced from compound 2) Check the activity series Determine which element is more active 3) Write the products and balance the equation If the more active element is already part of the compound then NO reaction will happen 4) Verify your results Make sure the equation is balanced (just like always)

58. Sample Problem E Let�s try one together Your turn!!!!

59. Double- Displacement Reactions Double- Displacement Reaction=> a reaction in which a gas, a solid precipitate, or a molecular compound forms from the apparent exchange of atoms or ions between two compounds Happens in aqueous solutions Must end up with a solid precipitate, gas, or molecular compound (like water)

60. Side Note In double- displacement reactions water, as a product, is often written as HOH so you can more easily see the exchange of atoms/compounds

61. Example HCl(aq) + NaOH(aq) -> HOH(l) + NaCl(aq) Notice how I put HOH This is a double replacement reaction The H and the Na changed partners You formed water (that�s one of the signs!!)

62. Skills Toolkit Page 284 Use this chart to help you identify reactions and predict products

63. �Writing Net Ionic Equations�Section 4 Goals Write total ionic equations for reactions in aqueous solutions Identify spectator ions and write ionic equations for reactions in aqueous solutions

64. Ionic Equations When ionic compounds dissolve in water, the ions separate form each other and spread throughout the solution So when you see KI(aq) what it really means is K+(aq) + I-(aq) Or if you see Pb(NO3)2(aq) it means Pb+2(aq) + 2NO3-(aq)

65. More Correct When we react the two compounds on the last slide we would do this: KI(aq)+ Pb(NO3)2(aq) -> PbI2(s) + 2KNO3(aq) But we should put the charges on them and then balance the charges and masses K+(aq) + I-(aq) + Pb+2(aq) + 2NO3-(aq) -> PbI2(s) + 2K+ (aq) + 2NO3-(aq)

66. Most Correct When you mix two solutions all of the ions are present in the combined solution But not all of the ions will react with each other Spectator ions=> ions that are present in a solution in which a reaction is taking place but that do not participate in the reaction These spectator ions can be taken out of the total ionic equation

67. Example Bottom of page 286

68. Writing Net Ionic Equations These equations only show the compounds that change

69. Displacement Net Ionic Happens in displacement reactions too Zn(s)+Cu+2(aq)+SO4-2(aq)-> Cu(s)+Zn+2 (aq)+ SO4-2(aq) Which is the spectator ion? How would we correctly write this?

70. Skills Toolkit Page 288 1) List what you know ID each chemical described ID type of reaction 2) Write a balanced equation Predict products Include states (next slide shows how to know!!!) 3) Write total ionic equation Write separated aqueous ions for each aqueous ionic substance DO NOT split up anything that is a solid, liquid, or gas 4) Find the net ionic equation Cancel out spectator ions Double check numbers and charges

71. Solubility All group 1 compounds and NH4 All nitrates All halides (but Ag+ and Pb+2) All sulfates (but Ca+2, Sr+2, Ba+2, Hg+2, and Pb+2) All carbonates (except group 1 and NH4) are INSOLUBLE!

72. Charges Make sure charges are equal on both sides SO4-2 (aq) + Ba+2 (aq) -> BaSO4(s) Notice no charge on reactant side so no charge on product side

73. Practice Br2(l) + NaI(aq) -> NaBr(aq) + I(s) Br2(l) + 2Na+(aq) + 2I-(aq) -> 2Na+(aq) + 2Br-(aq) + I2(s)