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Unit 8 Chemical Reactions

Unit 8 Chemical Reactions. PAGE 123. Describing Chemical Reactions. A chemical reaction is the process by which one or more substances are changed into one or more different substances. They are described by chemical equations. Describing Chemical Reactions. In a chemical reaction:

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Unit 8 Chemical Reactions

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  1. Unit 8 Chemical Reactions PAGE 123

  2. Describing Chemical Reactions • A chemical reactionis the process by which one or more substances are changed into one or more different substances. • They are described by chemical equations

  3. Describing Chemical Reactions • In achemical reaction: • bonds are broken in the reactants • Bonds are formed in the products

  4. Parts of a Chemical Equation

  5. Reactants • original substances in a chemical reaction • written on the left hand side of a chemical equation

  6. Products • The resulting substances produced in a chemical reaction. • written on the right hand side of the chemical equation

  7. yields

  8. Subscripts in (parenthesis) • represents the physical states of the compounds (elements) • Ex: (s)= solid, (l)=liquid, (g)= gas, (aq)= aqueous (dissolved in water)

  9. Words or symbols are placed over/under the arrow(s) to indicate certain conditions under which the reaction is carried out.

  10. : heat is applied • catalyst • substance that speeds up a chemical reaction withoutbecoming part of the reaction.

  11. Law of conservation of mass According to the law of conservation of mass, • the total mass of reactantsmustequal the total mass of products for any given chemical reaction.

  12. Law of conservation of mass Balance atoms H2(g) + O2(g) H2O (g) 2 2 Mass must be equal 50 g + 45 g  95g

  13. Translate Chemical Equations into Words

  14. Chemical Equations • 1) include all of the symbolsappearing in the equation (with the exception of the coefficients)

  15. Chemical Equations • 3. Diatomic Elements: Elements that combine with each other when found alone in nature

  16. Diatomic Elements • 7 diatomic elements (know) H2 O2 F2 Br2 I2 N2 Cl2

  17. Example #2 Mg(s) + 2HCl(aq) MgCl2(aq) + H2(g) reacts with Solid magnesium aqueous hydrochloric acid aqueous magnesium to produce chloride and hydrogen gas

  18. Check for Understanding CaCO3(s) CaO(s) + CO2(g) Solid calcium carbonate is heated and produces solid calcium oxide and gaseous carbon dioxide

  19. Check for Understanding #2 3KOH(aq) + Fe(NO3)3(aq) Fe(OH)3(s) + 3KNO3(aq) Aqueous potassium hydroxide reacts with aqueous iron (III) nitrate to produce solid iron (III) hydroxide and aqueous potassium nitrate

  20. Writing Chemical Equations from a Written Description

  21. Example #1 Aluminum metal reacts with oxygen in the air to form solid aluminum oxide. 4 Al (s) + O2(g) 3  2 Al2O3(s)

  22. Example #2 When solid mercury(II) sulfide is heated with oxygen gas, liquid mercury metal and gaseous sulfur dioxide are produced. HgS (s) + O2 (g) Hg (l) + SO2(g)

  23. Check for Understanding Oxygen gas can be produced by heating solid potassium chlorate in the presence of the catalyst manganese dioxide. Potassium chloride is a solid residue. MnO2 KClO3(s) KCl (s) + O2 (g) 2 2 3

  24. Check for Understanding Aqueous potassium nitrate and a precipitate of barium chromate are formed when aqueous solutions of barium nitrate and potassium chromate are mixed.

  25. Check for Understanding Aqueous potassium nitrate and a precipitate of barium chromate are formed when aqueous solutions of barium nitrate and potassium chromate are mixed. Ba(NO3)2(aq) + K2CrO4(aq)  2 KNO3(aq) + BaCrO4 (s)

  26. Types of Chemical Reactions

  27. Synthesis (Combination) Reactions Two or more substances combine to form a new compound. . Formation of only ONE product.

  28. Synthesis (Combination) Reactions

  29. Examples: 2H2 + O2 2H2O CaO + H2O Ca(OH)2

  30. Decomposition Reactions • A single compound undergoes a reaction that produces two or more simpler substances.

  31. Decomposition Reactions

  32. Decomposition Reactions Decomposition reactions are the opposite of synthesis reactions. There is only one reactant.

  33. Examples • CaCO3 CaO + CO2 • Na2CO3 Na2O + CO2

  34. Single-Replacement Reactions • one element replaces a similar element in a compound. • a single element reacts with a compound.

  35. Single-Replacement Reactions

  36. Distinguishing Characteristics • Examples: Pb + 2HNO3 Pb(NO3)2 + H2 F2 + 2NaI  2NaF + I2

  37. Predict the Products Zn + CuCl2 ZnCl2 + Cu

  38. Double Replacement Reactions The ions of two compounds exchange places in an aqueous solution to form two new compounds. Two ionic compounds “swap” ions.

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