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Nature of Chemical Reactions

Nature of Chemical Reactions. 5.1. Chemical Reactions. When substances undergo chemical changes, they form new substances. Atoms are rearranged, because bonds are broken and reformed. Chemical Reactions. Signs are: evolution of heat and light color change gases emitted

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Nature of Chemical Reactions

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  1. Nature of Chemical Reactions 5.1

  2. Chemical Reactions • When substances undergo chemical changes, they form new substances. • Atoms are rearranged, because bonds are broken and reformed

  3. Chemical Reactions • Signs are: • evolution of heat and light • color change • gases emitted • a precipitate (solid) forms

  4. Chemical Equations • Reactants substances that will undergo a chemical change. (Left side)

  5. Chemical Equations • Products substances that are formed as a result of a chemical change. (Right side)

  6. Examples • water + mix+ eggs→ cake • 6CO2 + 6H2O→ C6H12O6 +6O2 Reactants Products

  7. Energy and Reactions • Every reaction needs energy to get things started. • This energy is needed to break the chemical bonds of the reactants.

  8. Energy and Reactions • Usually comes in the form of heat, electricity, sound or light.

  9. Chemical Energy • Energy stored within an atom and is released when a substance reacts. • Stored energy is known as Potential Activation Energy

  10. No reaction takes place Reaction takes place

  11. Endothermic reaction • Reaction where heat energy is absorbed. • Surroundings get colder • chemical energy of products greater than reactants

  12. Examples • Ice pack placed on your skin • Photosynthesis • NH4NO3 reacting with water becomes very cold

  13. Exothermic Reaction • Reaction where heat energy is released • surrounding get hotter • Chemical energy of reactants greater than products reactants

  14. Examples • Match being lit • Firecracker exploding • NaOH reacting with water will get hotter.

  15. Reaction Types 5.2

  16. Synthesis Reaction • A reaction when two substances form at least one new, more complex compound.

  17. Synthesis Reaction • two or more reactants = one product

  18. Synthesis Reaction • EXAMPLE: A + B A B 2Fe + O22FeO

  19. Decomposition Reaction • A reaction in which one compound breaks into at least two products. • Reactant decomposes into parts

  20. Decomposition Reaction • one reactant = two or more products

  21. Decomposition Reaction EXAMPLE: ABA + B 2 NI3N2 + 3I2

  22. Combustion reaction • Reaction in which a compound and oxygen burn. • Oxygen (O2) always is a reactant

  23. Combustion reaction • CO or CO2 will always be a product • H2O will always be a product

  24. Combustion reaction C2H50H + 3O2  2CO2 + 3H2O

  25. A reaction in which atoms of one element take the place of atoms of another compound. Single displacement Reaction

  26. Example X A + B B A + X 3CuCl2 + 2Al  2AlCl3 + 3Cu Single displacement Reaction

  27. Double Replacement Reaction • A reaction in which the apparent exchange of ions between two compounds.

  28. Double replacement reaction AX + BY AY + BX Pb(NO3)2+K2(CrO4) → Pb(CrO4)+2K(NO3)

  29. Balancing Chemical Equations 5.3

  30. Balancing • All equations must have the same type and number of atoms on each side of the equation. • Law of Conservation of Mass • Tells you the amounts

  31. Rule to Balancing • Can only change coefficients and never subscripts. • Always balance H and O last if water is in the equation. • Balance the polyatomic ions first if present

  32. Mole Ratios • Coefficients show the amount of moles of each substance. • Mole ratio is the smallest relative number of moles of the substance involved in a reaction. • 2H2 + O2 → 2H2O = 2:1:2

  33. P 165

  34. Rates of Change 5.4

  35. What is a Rate? • The speed at which it takes something to occur. • It is not a time!!!!! • m/s, mi/hr, potato/min

  36. Factors Affecting RXN Rates • Temperature • Surface Area • Concentration • Catalysts

  37. Temperature • Higher the temperature the faster the reaction. • Higher temperature causes particles to move faster.

  38. Surface Area • The amount of particles that are exposed. • The greater the surface area the faster the reaction. • Breaking things into pieces increases thesurface area.

  39. Concentration • The more concentrated the solution the faster the reaction will be. • More concentrated = less diluted.

  40. More concentrated Which has a higher concentration of reactants?

  41. Catalyst • A substance that changes the rate of chemical reactions without being consumed.

  42. Catalyst • Catalysts speed up reactions. (enzymes) • Inhibitors slow down reactions (preservatives)

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