2. Chemical Reactions

3. BELLWORK BRIEFLY WRITE ABOUT A SCIENTIFIC OBSERVATION YOU MADE RECENTLY

4. Chemical equations WE USE CHEMICAL EQUATIONS TO DESCRIBE CHEMICAL REACTIONS

5. Burning Coal

6. This is a chemical reaction The purpose of the equation is to show what was present before the reaction (carbon and oxygen) and afterwards (carbon dioxide)

7. The substances that undergo change are reactants (carbon and oxygen) New substances formed as a result of that change are called products REACTANTS PRODUCTS

8. CARBON + OXYGEN CARBON DIOXIDE SIMPLIFY: C+O 2 CO 2

9. CHEMICAL EQUATION A CHEMICAL EQUATION IS A REPRESENTATION OF A CHEMICAL REACTION IN WHICH THE REACTANTS AND PRODUCTS ARE EXPRESSED AS FORMULAS.

10. CONSERVATION OF MASS THE LAW OF THE CONSERVATION OF MASS: MASS IS NEITHER CREATED NOR DESTROYED IN A CHEMICAL REACTION ALTHOUGH THE MASS OF THE COAL WAS REDUCED DURING THE REACTION, IT WAS NOT LOST THE MASS OF THE CARBON DIOXIDE CREATED WAS EQUAL TO THE MASS OF THE COAL THAT WAS LOST

11. BALANCING EQUATIONS ACCORDING TO THE LAW OF CONSERVATION OF MASS, EACH SIDE OF AN EQUATION MUST BE EQUAL H 2 + O 2 H 2 O WHAT IS WRONG WITH THIS EQUATION?

12. TO BALANCE WE SIMPLY ADD COEFFICIENTS: THE NUMBERS THAT APPEAR BEFORE THE EQUATION H 2 + O 2 H 2 O= H 2 + O 2 2H 2 O WHAT IS WRONG WITH THIS EQUATION? HOW CAN WE FIX IT?

13. ANSWER 2H 2 + O 2 2H 2 O WHICH MEANS: TWO MOLECULES OF HYDROGEN REACT WITH ONE MOLECULE OF OXYGEN TO YIELD TWO MOLECULES OF WATER

14. http://PHSchool.com/webcodes10/index.cfm?wcprefi x=ccp&wcsuffix=1071&area=view&x=13&y=7

15. MATH SKILLS READ OVER THE MATH SKILLS EXAMPLES AND STEPS FOR BALANCING EQUATIONS ON PAGE 195 THEN, TRY THE MATH PRACTICE 1-3

16. Balancing equations tutorials http://www.youtube.com/watch?v=RnGu3xO2h74 http://www.youtube.com/watch?v=gskm-dfKv5g

17. BELLWORK BALANCE THE FOLLOWING CHEMICAL EQUATION: H 2 +O 2  H 2 O

18. WHAT ARE SOME UNITS OF MEASURE THAT YOU KNOW OF?

20. A. What is the Mole? A counting number (like a dozen) Avogadro ’ s number (N A ) 1 mol = 6.02  10 23 items A large amount!!!!

21. Counting with Moles MOLE: (MOL) AN AMOUNT OF A SUBSTANCE THAT CONTAINS APPROXIMATELY 6.02 X 10 23 PARTICLES OF THAT SUBSTANCE. KNOWN AS AVOGADRO’S NUMBER A MOLE OF A SUBSTANCE GENERALLY CONTAINS 6.02 X 10 23 ATOMS, MOLECULES, OR IONS OF THAT SUBSTANCE

23. n 1 mole of hockey pucks would equal the mass of the moon! A. What is the Mole? 1 mole of pennies would cover the Earth 1/4 mile deep! n 1 mole of basketballs would fill a bag the size of the earth!

25. Molar Mass THE MASS OF DIFFERENT ELEMENTS ARE DIFFERENT, AS IS THEIR MOLAR MASS THE MOLAR MASS OF AN ELEMENT IN THE SAME AS ITS ATOMIC MASS EXPRESSED IN GRAMS

26. MASS OF COMPOUNDS YOU CAN FIND THE MASS OF COMPOUNDS BY ADDING THE MASS OF THEIR COMPONENTS A CARBON DIOXIDE MOLECULE: CARBON= 12 GRAMS OXYGEN = 16 GRAMS X 2 = 32 GRAMS 12 + 32 = 44 GRAMS CARBON DIOXIDE HAS A MOLAR MASS OF 44 GRAMS

27. LETS TRY MOLAR MASS OF C MOLAR MASS OF Fe MOLAR MASS OF H 2 O

28. MOLE-MASS CONVERSIONS TO FIND HOW MANY MOLES ARE IN A CERTAIN # OF GRAMS OF AN ELEMENT OR MOLECULE: Y GRAMS x1/z grams= x moles

30. Example WE HAVE 55 GRAMS OF CO 2 HOW DO WE FIND HOW MANY MOLES WE HAVE? 55 X 1 mol/44 g 1 mol/44 g=.02272727 mol.02272727mol X 55 g = 1.25 mol CO 2

31. BELLWORK WHAT IS A MOLE? WHY DO WE USE MOLES? HOW MUCH IS ONE MOLE OF BARIUM IN GRAMS? CARBON DIOXIDE? WATER?

32. REVIEW: A mole is just a number, nothing else That number is 6.02 x 10 23 We use this number to make otherwise incredibly small numbers (such as the mass of an atom) easy to use in chemical formulas

33. Review There are two conversions we will do with moles: Find how many moles there are in a certain number of grams (mass) an element or molecule Find the the number of grams (mass) there are in a certain number of moles of an element or molecule

34. Two conversion factors a)Gramsb) 1 Mol 1 Molor Grams How many grams, use conversion factor a How many moles, use conversion factor b

35. Practice Suppose we have 55 grams of CO 2 How do we find how many moles of CO 2 there are in 55 grams of CO 2 ? Step 1: find the molar mass of CO 2 44 grams/mole Step 2: set up the equation 55 grams CO 2 x 1 mol CO 2 = ? mol CO 2 44 grams CO 2

36. Step 3: Solve the equation 55 grams CO 2 x 1 mol CO 2 = ? mol CO 2 44 grams CO 2 1/44=.0227 55 x.0227 = 1.25 There are 1.25 moles of CO 2 in 55 grams of CO 2

37. Flip it! Now, suppose we have 2.4 moles of sulfur. How do we find how many grams there are in 2.4 moles of sulfur? Step 1: Find the molar mass of sulfur. 32.07 grams/mole Step 2: Set up the equation: 2.4 moles x 32.07 grams S = ? Grams S 1 mol S

38. Step 3: solve the equation: 2.4 x 32.07 = 77 grams sulfer There are 77 grams of sulfur in 2.4 moles of sulfur

39. Get into the groups I assigned the other day. Work on the worksheet together. Do as many problems as you can.

40. Types of Chemical Reactions http://www.youtube.com/watch?v=i-HHvx1VC_8 http://www.youtube.com/watch?v=nsEkKIiOz7Q

41. 7.2 Types of Chemical Reactions Just like states of matter, you can classify chemical reactions based on reactants and products. Types: Synthesis Decomposition Single-replacement Double replacement Combustion

42. Flip Book Time! Make a flip book for the different types of chemical reactions. You should have 6 flaps, 1 title and 5 different reactions Each flap should have: The type of reaction (Synthesis) Definition/explanation Real example (Sodium reacts with chlorine to produce sodium chloride) Chemical example (A + B -> AB)

43. Finished? Complete your workbook up to section 7.2 We will have an open note quiz over balancing chemical equations and mole conversions tomorrow.

44. Synthesis Reaction where two or more substances react to form a single substance. A + B -> AB Reactants may be elements or compounds Examples: sodium reacts with chlorine to make sodium chloride Chemical Example: 2NA + Cl 2 -> 2NaCl

45. Synthesis

47. DECOMPOSITION A COMPOUND BREAKS DOWN INTO TWO OR MORE SIMPLER SUBSTANCES AB -> A + B REACTANTS MUST BE COMPOUNDS PRODUCTS MAY BE COMPOUNDS OR ELEMENTS EXAMPLE: WATER DECOMPOSES INTO HYDROGEN AND OXYGEN GAS WHEN ELECTRICITY IS PASSED THROUGH IT 2H 2 O -> 2H 2 + O 2

48. Decomposition

50. SINGLE REPLACEMENT REACTION WHERE ONE ELEMENT TAKES THE PLACE OF ANOTHER IN A COMPOUND A + BC -> B + AC EXAMPLE: COPPER WIRE IS DIPPED INTO SILVER NITRATE AND WATER. COPPER REPLACES THE SILVER IN SILVER NITRATE TO FORM COPPER (II) NITRATE. Cu + 2 AgNO 3 -> 2Ag + Cu(NO 3 ) 2

52. Double Replacement Two different compounds exchange positive ions and form two new compounds AB + CD -> AD +CB Example: Lead (II) nitrate and potassium iodide (colorless). Yellow precipitate forms Pb(NO 3 ) 2 + 2KI -> PbI 2 + 2KNO 3

55. Combustion A substance reacts rapidly with oxygen, often producing heat and light Example: burning of natural gas CH 4 + 2O 2 -> CO 2 + 2H 2 O

56. Oxidation - Reduction A reaction in which electrons are transferred from one reactant to another is a oxidation-reduction reaction Oxidation and reduction always occur together It can involve full transfers, or partially charged elements.

57. Oxidation Any process in which an element loses electrons during a chemical reaction is oxidation

58. Reduction The process in which an element gains electrons during a chemical reaction is called reduction. Reactants are said to be reduced if they gain electrons

59. Bellwork What is all involved in a chemical equation? Reactants Products Energy

60. 7.3 Energy Changes in Reactions Key concepts: What happens to chemical bonds during a chemical reaction? What happens to energy during a chemical reaction?

61. Example Lighting a gas grill, this is a chemical reaction What are the reactants? Propane and oxygen What are the products? Carbon dioxide and water What else is there? Heat!

62. Where does the heat come from? Chemical energy is stored in the chemical bonds of a substance. Chemical reactions involve the breaking of chemical bonds in the reactants and the formation of chemical bonds in the products

63. Combustion of Propane

64. *During the combustion of propane the bonds in propane and oxygen molecules are broken, while the bonds in carbon dioxide and water molecules are formed.

65. Breaking bonds 8 C-H, 5 O=O6 C=O 8 O-H 2 C-C

66. Breaking bonds Breaking bonds requires energy This is why a propane grill must have an igniter, to provide energy to get the reaction started

67. Forming Bonds Once the bonds of the reactants are ignited, the bonds are broken, a chemical reaction occurs, and products come together. The products created from a chemical reaction are bonded together Energy is released when these bonds are created. This energy is heat and light.

68. Question Does breaking bonds require energy or release energy? It requires energy.

69. Review In an Endothermic reaction (such as freezing) energy is released into the surroundings In an Exothermic reaction (such as melting) energy is absorbed from the surroundings.

70. Exothermic/Endothermic Reactions During a chemical reaction, energy is either released or absorbed A chemical reaction that releases energy into its surroundings is an exothermic reaction

71. Exothermic Exothermic reactions release more energy than is required to break the bonds of the reactants Combustion is an example of an exothermic reaction

72. Exothermic In any reaction, the chemical energy reaches a peak before the reactants change into products. For example, at room temperature the propane molecules and oxygen molecules will not collide with enough energy to cause a reaction They need the help/heat/energy of a spark to begin the reaction

73. Exothermic In your book on pg 208, figure A shows a graph that describes the reaction process. The equation is written A+B-> AB J

74. Endothermic Reactions A chemical reaction that absorbs energy from its surroundings is an endothermic reaction In an endothermic reaction, more energy is required to break the bonds in the reactants than is released by the formation of the products.

75. Endothermic Look at 208, figure B You can see the difference between the reactants and products Decomposition is a type of endothermic reaction The equation is written A + B J -> AB

76. Conservation of Energy The total amount of energy before and after the reaction is the same. Complete 7.3 in your workbook for homework or in class if we have time