Chapter 14 Chemical Reactions
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Chapter 14 Chemical Reactions

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Chapter 14 Chemical Reactions Presentation Transcript

  • 1. Liberty Christian Academy
    General Chemistry
    Miss Kostura
    Chapter 14Chemical Reactions
  • 2. Forming New Substances
    What is the difference?
  • 3. Forming New Substances
    • Leaves change colors in the fall… but what is happening to cause this change?
    • 4. Leaves contain a compound called chlorophyll. Chlorophyll undergoes a chemical change and forms simpler substances that have no color.
  • Forming New Substances
    • You see the red, orange, and yellow colors because the green color of the chlorophyll no longer hides them.
  • Forming New Substances
    • Leaves changing colors in the fall are an example of a chemical reaction.
    def: the process by which one or more substances undergo change to produce one or more different substances.
    • Recall, the new substances have different chemical and physical properties.
  • Forming New Substances
    • Examples of chemical reactions…
  • Forming New Substances
    • Clues to help you recognize a chemical reaction
    Gas formation
    Solid formation
    Color change
    Energy change
  • 5. Forming New Substances
    • Carbon dioxide (CO2) is great… here’s why!
    • 6. Dissolved under pressure = carbonated beverages
    • 7. CO2 gas is not combustible & is denser than air= fire extinguishers
    • 8. dry ice/solid CO2 = cooling effect, better than ice
    • 9. sublimes… very useful… no watery mess!
  • Forming New Substances
    • New substances form because chemical bonds in the starting substance break.
    • 10. Then atoms rearrange.
    • 11. Finally, a new bond forms in the new substance.
  • Forming New Substances
    • Remember… a chemical symbol is shorthand for writing an element.
    • 12. Oxygen = O
    • 13. Nitrogen = N
    • 14. Carbon = C
  • Forming New Substances
    • Chemical formula
    def: a shorthand way of writing a compound or a diatomic element using chemical symbols and numbers.
    Example: H2O, CO2, C6H12O6
  • 15. Forming New Substances
    • the number represents how many of each kind of atom is present in a molecule.
    • 16. H2O tells you that a water molecule is composed of 2 hydrogen atoms and 1 oxygen atom.
    • 17. The 2 is a subscript. Subscripts are written below and to the right of a chemical symbol.
  • Forming New Substances
    • When no subscript is present after a symbol… it indicates only one atom of the element.
    • 18. Example: H2O, N2O
  • Forming New Substances
    • Let’s try a compound a little more difficult… how many atoms of each element are in this formula?
    • 19. Na2SO4
    • 20. Ca(NO3)2
  • Forming New Substances
    Writing Formulas for Covalent Compounds
    • The prefix used in the name represents the number of atoms in that compound.
  • Forming New Substances
    Prefixes to memorize
    mono- 1
    di- 2
    tri- 3
    tetra- 4
    penta- 5
    hexa- 6
  • 21. Forming New Substances
    • How to write a chemical formula from the name of a covalent compound
    • 22. The lack of a prefix indicates only 1 atom.
    • 23. The prefix di indicates 2 atoms… etc.
    Example: carbon dioxide = CO2
    dinitrogen monoxide = N2O
  • 24. Forming New Substances
    Writing Formulas for Ionic Compounds
    • If the name contains a metal and nonmetal… the compound is probably ionic.
  • Forming New Substances
    Here’s how…
    Make sure the overall charge is zero.
    The formula may need subscripts to cause the charges of the ions to cancel out. (Remember… the charge of many ions can be determined by looking at the periodic table.)
    Example: Mg is in column 2, it has a +2 charge.
  • 25. Forming New Substances
    Practice
    • Sodium Chloride – NaCl
    sodium ion has 1+ charge
    chloride ion has a 1- charge
    ** one sodium ion & one chloride ion have an overall charge of zero*** (+1) + (-1) = 0
  • 26. Forming New Substances
    Practice
    • Magnesium Chloride - MgCl2
    magnesium ion has a 2+ charge
    chloride ion has a 1- charge
    ** one magnesium ion & two chloride ions have an overall charge of zero** (+2) + 2(-1) = 0
  • 27. Forming New Substances
    • How do all chemists know what each other means?
    chemical equation
    def: a shorthand description of a chemical reaction using chemical formulas and symbols.
    • This form is understood around the world and needs no explanation.
  • Forming New Substances
    • Chemical reactions involve two sides of the equation.
    Reactants yield Products
    Reactants Products
    Reactants- starting materials
    Products- substances formed from a reaction
  • 28. Forming New Substances
    Reactants Products
    Example: C + O2 CO2
    Charcoal for barbecuing contains C. The C reacts with O in the air, and the primary product is CO2.
  • 29. Forming New Substances
    • Make sure you are accurate in writing the substances of a reaction carefully.
    • 30. Remember to use the proper chemical symbol.
    MISTAKES… CO2 vs. CO vs. Co
    • Don’t forget to write a subscript of 2 for the diatomic elements.
    ( 7 total: H2, N2, O2, F2, Cl2, Br2, I2 )
  • 31. Forming New Substances
    • What about hydrogen gas, H2, as fuel for vehicles.
    • 32. Mode: as H burns, water is the only product.
    • 33. Benefits: cheaper, less air pollution.
  • Forming New Substances
    An equation MUST BE BALANCED!!!
    • Every atom in the reactants becomes part of the products.
    • 34. Atoms are never lost or gained in a chemical equation.
    • 35. The number of atoms of each element on the reactants side must equal the number of atoms of the same elements on the products side.
  • Forming New Substances
    Remember…
    • You CAN NOT CHANGE SUBSCRIPTS
    • 36. You can change coefficients
  • Forming New Substances
    • French chemist, Antoine Lavoisier (1700’s) performed experiments and determined that the total mass of reactants equaled the total mass of the products.
    Law of conservation of mass
    def: mass is neither created nor destroyed in ordinary chemical and physical changes
  • 37. Forming New Substances
    • Therefore… a chemical equation must have the same number and kind of atom on both sides.
    Example: 2H2 + O2 2H2O
  • 38. Forming New Substances
    Review Questions
    Page 357 #1 - 5
  • 39. Types of Chemical Reactions
    Types of Chemical Reactions
    Synthesis Reactions
    Decomposition Reactions
    Single-Replacement Reactions
    Double-Replacement Reactions
  • 40. Types of Chemical Reactions
    What happens when something decomposes?
    What happens when something synthesizes?
  • 41. Types of Chemical Reactions
    Synthesis Reaction
    def: a reaction in which two or more substances combine to form a single compound.
    Example: A + B AB
    2Na + Cl2 2NaCl
  • 42. Types of Chemical Reactions
    Decomposition Reaction
    def: a reaction in which a single compound breaks down to form two or more simpler substances.
    Example: AB A + B
    H2CO3 H2O + CO2
  • 43. Types of Chemical Reactions
    Single-Replacement Reaction
    def: a reaction in which an element takes the place of another element that is part of a compound.
    Note: the products are a new compound and a different element.
    Example: A + BC AC + B
    Zn + 2HCL ZnCl2 + H2
  • 44. Types of Chemical Reactions
    Double Replacement Reaction
    def: a reaction in which ions in two compounds switch places. One of the products of this reaction is often a gas or a precipitate.
    Example: AB + CD AD + CB
    NaCl + AgFNaF + AgCl
  • 45. Types of Chemical Reactions
    Review Questions
    Page 360 # 1 & 2
  • 46. Energy & Rates of Chemical Reactions
    • Every chemical reaction involves chemical ENERGY!
    • 47. During a reaction, the chemical bonds that hold the reactants together are broken as they absorb energy.
    • 48. When new bonds form in the products, the energy is released.
  • Energy & Rates of Chemical Reactions
    • If the reactants contain more chemical energy than the products… energy will be released during the reaction… this is called exothermic.
    def: a chemical reaction in which energy is released or removed.
  • 49. Energy & Rates of Chemical Reactions
    • This energy can be released in several different forms… such as light, electrical, or thermal.
    2Na + Cl2 2NaCl + energy
    • Example: Campfire (light & thermal energy are released)
  • Energy & Rates of Chemical Reactions
    • If the reactants contain less chemical energy than the products… energy is absorbed during the reaction… this is called endothermic.
    def: a chemical reaction in which energy is absorbed.
  • 50. Energy & Rates of Chemical Reactions
    • Written as…
    2H2O + energy 2H2 + O2
    Example: Photosynthesis… plants use energy from the sun
    6CO2 + 6H2O + energy C6H12O6 + 6O2
  • 51. Energy & Rates of Chemical Reactions
    • Just like mass is never created or destroyed in chemical reactions… the same is true for energy.
    • 52. Law of conservation of energy
    def: energy can neither be created or destroyed
  • 53. Energy & Rates of Chemical Reactions
    • The energy that is released in an exothermic reaction was originally stored in the reactants.
    • 54. The energy absorbed in an endothermic reaction is used to fuel the reaction and ends up in the products.
  • Energy & Rates of Chemical Reactions
    • All substances need energy to start a reaction.
    Example: a match contains all the reactants needed to burn, but it will not burn until energy is added. This energy comes from the friction of striking it.
    Activation energy
    def: the minimum amount of energy needed for substances to react.
  • 55. Energy & Rates of Chemical Reactions
    • Example: an electric spark in a car’s engine provides activation energy to begin the burning of gasoline.
  • Energy & Rates of Chemical Reactions
    • Look at 2 diagrams on page 363…
  • Energy & Rates of Chemical Reactions
    • Factors affecting rates of reactions- measure of how rapidly the reaction takes place.
    Temperature
    Concentration
    Surface area
    Catalyst or Inhibitor
  • 56. Energy & Rates of Chemical Reactions
    • Temperature- increasing the temperature makes particles move faster… increase rate of reaction.
    temperature = rate of reaction
  • 57. Energy & Rates of Chemical Reactions
    • Concentration- increase the number of reactant particles… increase rate of reaction*.
    concentration = rate of reaction
    *Note- there are always a few exceptions.
  • 58. Energy & Rates of Chemical Reactions
    • Surface area- increase the amount of exposed surface of a solid reactant… increases rate of reaction.
    surface area = rate of reaction
  • 59. Energy & Rates of Chemical Reactions
    • Some reactions occur too slow for us… so we need to use a catalyst.
    Catalyst- a substance that speeds up a reaction without being permanently changed.
  • 60. Energy & Rates of Chemical Reactions
    • Most reactions in your body are sped up using catalysts called enzymes.
    • 61. Everything your body does involves an enzyme.
  • Energy & Rates of Chemical Reactions
    • Amylase- an enzyme in your saliva necessary for digestion of food… it’s starts working as soon as the food enters your mouth.
  • Energy & Rates of Chemical Reactions
    • Inhibitor- substance that slows down or stops a chemical reaction.
    • 62. Example: preservatives added to foods are inhibitors that slow down the rates of bacteria or fungus which spoils food.
  • Energy & Rates of Chemical Reactions
    • Review Questions
    Page 365 # 1, 2, & 4
  • 63. Energy & Rates of Chemical Reactions
    Chapter Review Quesitons
    Page 368 # 1-13, 15, 17-19, 21