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Chapter Five

Chapter Five. Chemical Quantities and Reactions The Mole Molar Mass Chemical Changes Chemical Equations Types of Reactions Mole Relationships in Chemical Equations Mass Calculations Energy in Chemical Reactions. The Mole. Many things have names for a quantity or group.

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Chapter Five

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  1. Chapter Five • Chemical Quantities and Reactions • The Mole • Molar Mass • Chemical Changes • Chemical Equations • Types of Reactions • Mole Relationships in Chemical Equations • Mass Calculations • Energy in Chemical Reactions

  2. The Mole • Many things have names for a quantity or group. • In chemistry, a quantity of atoms, molecules, etc. is called a mole.

  3. The Mole • Why a “mole”?

  4. The Mole • A mole of anything is 6.02 E+23 particles. • This is sometimes referred to as Avogadro’s Number. • Written as a number: • 602,000,000,000,000,000,000,000 • A mole of marbles would easily fill the entire Grand Canyon with much to spare.

  5. The Mole • One mole of: • Carbon = 6.02 E+23 carbon atoms • CO2 =6.02 E+23 CO2 molecules • NaCl = 6.02 E+23 NaCl formula units • 1 mole of anything = 6.02 E+23 particles

  6. Learning Check • Ex) Convert 0.0242 moles of CH4 to molecules.

  7. Learning Check • Ex) Convert 4.45 E+21 atoms of Zn to moles.

  8. Subscripts and Moles • The subscripts in a formula can be interpreted on either an atom or mole level. • Ex) C6H12O6

  9. Learning Check • Ex) How many moles of H atoms are present in 0.0150 moles of NH3? How many H atoms?

  10. Molar Mass • A molar mass of an element is the atomic mass expressed in grams. • The molar mass of carbon is 12.01g

  11. Molar Mass • The molar mass of any compound is equal to the sum of all the atomic weights for each element in the formula. • Ex) The molar mass of CO2 is: 1C + 2O = 1(12.0g) + 2(16.0g) = 44.0g Thus, 1 mole of CO2 = 44.0g

  12. Learning Check • What is the molar mass of MgCl2? • 94.0g • 59.8g • 95.3g • 119.6g

  13. Learning Check • What is the molar mass of Al(OH)3? • 78.0g • 46.0g • 132.0g • 44.0g

  14. Molar Mass • Any molar mass can written as a conversion factor. • From earlier: • 1 mole of CO2 = 44.0g

  15. Molar Mass • This allows for the conversion between grams and moles. • Ex) 45.0g of BaCl2 = ? moles

  16. Molar Mass • Ex) 1.52 x 10-3 moles of phosphorous tribromide = ? grams

  17. Moles • Combining both molar mass and Avogadro’s number concepts.

  18. Learning Check • An 8.15 E+21 molecules of C2H6 would have a mass of:

  19. Learning Check • A 45.3g sample of lead(II) chloride would contain how many formula units?

  20. Learning Check • A 6.50 x 10-5 g sample of C5H10O5 will contain how many Hydrogen atoms?

  21. Physical Changes • A physical change is one in which the state, shape, or size of the substance is altered but not its identity. • Ex) Ice melting • Ex) Ripping a piece of paper • Ex) Boiling ethanol • Ex) Pulverizing a rock

  22. Chemical Changes • A chemical change is one in which matter is transformed into new kinds of matter by the rearrangement of atoms. • Ex) Iron rusting • Ex) Burning a log • Ex) Fermenting grapes • Ex) Antacid neutralizing stomach acid

  23. Learning Check • Decide whether each is Physical or Chemical change. • a) Making Kool-aid • b) Baking cookies • c) Cutting an aspirin in half • d) Bleaching a stained shirt

  24. Chemical Equations • Shows the before and after for a chemical reaction using chemical formulas.

  25. Chemical Equations • Symbols added having various meanings.

  26. Chemical Equations • A Chemical Equation is always written so that the total numbers of atoms on each side of the equation are equal. • To do this, coefficients are added in front of each substance. • Must use lowest whole number coefficients!

  27. Chemical Equations • __Al + __Cl2  __AlCl3 • Reaction is NOT balanced! • Note: can NOT alter any subscripts! • Make a tally sheet.

  28. Learning Check • Balance the following: • __FeCl2 + __Al  __AlCl3 + __Fe • __Al2(SO4)3 + KOH  Al(OH)3 + K2SO4

  29. Learning Check • Balance the following: • __H3PO3  __H3PO4 + __PH3 • __C3H8 + __O2  __CO2 + __H2O

  30. Learning Check • Balance the following: • __C4H8O + __O2  __CO2 + __H2O

  31. Types of Reactions • Combination Reaction • 2Al(s) + 3Br2(l)  2AlBr3(s) • CaO(s) + CO2(g)  CaCO3(s)

  32. Types of Reactions • Decomposition Reaction • (NH4)2Cr2O7(s)  Cr2O3(s) + 4H2O(g) + N2(g)

  33. Types of Reactions • Single Replacement Reactions • Mg(s) + CuCl2(s)  MgCl2(s) + Cu(s)

  34. Types of Reactions • Double Replacement Reactions • Pb(NO3)2(aq) + K2CrO4(aq)  PbCrO4(s) + 2KNO3(aq)

  35. Combustion • A rapid reaction with oxygen from the air. • CH4(g) + 2O2(g)  CO2(g) + 2H2O(l) • Also occurs in the cells of animals when glucose, C6H12O6, is converted to energy.

  36. Chemical Reactions • A reaction can be interpreted in many ways. • Atoms and molecules • Moles • Masses

  37. Chemical Reactions • N2 + 3 H2 2 NH3 • Molecular interpretation • Mole interpretation • Mass interpretation

  38. Law of Conservation of Mass • In any chemical reaction, matter cannot be created nor destroyed. • Masses of reactants = Masses of products.

  39. Stoichiometry • The calculation of chemical quantities in a reaction. • Relates a mass of a reactant or product to any other reactant or product.

  40. Stoichiometry Mass of A Mass of B Moles of A Moles of B

  41. Stoichiometry • If 45.1g of N2 are used, then what mass of H2 is required?

  42. Stoichiometry • If 7.25g of H2 completely reacts, what mass of NH3 is produced?

  43. Stoichiometry • For the reaction: • 2C2H2 + 5O2 4CO2 + 2H2O • If 6.85g of C2H2 is completely combusted, then what mass of CO2 is produced? • a. 13.7g • b. 11.6g • c. 23.2g • d. 5.80g

  44. Stoichiometry • For the reaction: • 4Al + 3O2 2Al2O3 • When 0.452g of Al completely reacts, what mass of Al2O3 is produced? • a. 3.42g • b. 0.853g • c. 0.226g • d. 23.1g

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