5.1 Introduction to Chemical Reactions A. General Features of Physical and Chemical Changes

1. 5.1 Introduction to Chemical ReactionsA. General Features of Physical and Chemical Changes • A chemical change (a chemical reaction) converts one substance into another. • Chemical reactions involve: • Breaking bonds in the reactants (starting materials) • Forming new bonds in the products

2. 5.1 Introduction to Chemical ReactionsA. General Features of Physical and Chemical Changes

3. 5.1 Introduction to Chemical ReactionsB. Writing Chemical Equations A chemical equation uses chemical formulas and othersymbols showing what reactants are the starting materials in a reaction and what products are formed.

4. 5.1 Introduction to Chemical ReactionsB. Writing Chemical Equations • The law of conservation of mass states that atoms cannot be created or destroyed in a chemical reaction.

5. 5.1 Introduction to Chemical ReactionsB. Writing Chemical Equations

6. 5.2 Balancing Chemical Equations HOW TO Balance a Chemical Equation Write a balanced chemical equation for the reaction of propane (C3H8) with oxygen (O2) to form carbon dioxide (CO2) and water (H2O). Example Step [1] Write the equation with the correct formulas.

7. 5.2 Balancing Chemical Equations HOW TO Balance a Chemical Equation Balance the equation with coefficients one element at a time. Step [2] • Balance the C’s first: • Balance the H’s next:

8. 5.2 Balancing Chemical Equations HOW TO Balance a Chemical Equation Balance the equation with coefficients one element at a time. Step [2] • Finally, balance the O’s:

9. Balance the Equations __H2+ __O2 __H2O __NO + __O2  __NO2 __CH4 + __Cl2  __CH2Cl2 + __HCl

10. Polyatomic Ions __Ca3(PO4)2 + __H2SO4 __CaSO4 + __H3PO4

11. Balance the Equation __Al + __H2SO4 __Al2(SO4)3 + __H2 __Na2SO3 + __H3PO4  __H2SO3 + __Na3PO4

12. Balance the Equation __Mg + __HBr __MgBr2 + __H2 __KClO3  __KCl + __O2 __CH4 + __Cl2 __CCl4 + __HCl

13. Balance the Equation __Al2O3 + __HCl  __AlCl3 + __H2O __Al(OH)3 + __H2SO4  __Al2(SO4)3 + __H2O

14. __Ni + __HCl  __NiCl2 + __H2 __PbS + __O2  __PbO + __SO2 __H3PO4 + __Ca(OH)2  __Ca3(PO4)2 + __H2O

15. __H2SO4 + __NaOH  __Na2SO4 + __H2O __CO + __O2  __CO2 __S + __O2 + __H2O  __H2SO4

16. 5.3 Types of Reactions The majority of chemical reactions fall into 6 categories: • combination • decomposition • single replacement • double replacement • oxidation and reduction (Section 5.4) • acid-base (Chapter 9)

17. 5.3 Types of ReactionsA. Combination and Decomposition • A combination reaction is the joining of two or more reactants to form a single product.

18. 5.3 Types of ReactionsA. Combination and Decomposition • A decomposition reaction is the conversion of a single reactant to two or more products.

19. 5.3 Types of ReactionsB. Replacement Reactions • A single replacement reaction is a reaction in which one element replaces another element in a compound to form a different compound and element as products.

20. 5.3 Types of ReactionsB. Replacement Reactions

21. 5.3 Types of ReactionsB. Replacement Reactions • A double replacement reaction is a reaction in which two compounds exchange “parts”–atoms or ions—to form two new compounds.

22. 5.3 Types of ReactionsB. Replacement Reactions

23. Combination, Decomposition, Single Displacement or Double Displacement? Ni(NO3)2 + Mg  Ni + Mg(NO3)2 2 KI + Sn(NO3)2  SnI2 + 2 KNO3 2 HgO  2 Hg + O2

26. Predicting Reactions Combination: N2 + ____  Mg3N2 Decomposition: 2 SO3  2SO2 + ______ Single Replacement: 2 Ag + CuBr2  ______ + ______ Double Replacement: KOH + HI  ______ + _______

28. 5.4 Oxidation and ReductionA. General Features • Oxidation is the loss of electrons from an atom. • Reduction is the gain of electrons by an atom. • Both processes occur together in a single reaction called an oxidation−reduction or redox reaction. • A redox reaction involves the transfer of electrons from one element to another. • A redox reaction always has two components, one that is oxidized and one that is reduced.

29. 5.4 Oxidation and ReductionA. General Features

30. 5.4 Oxidation and ReductionA. General Features Zn2+ + Cu Zn + Cu2+ Each of these processes can be written as an individual half reaction: Oxidation half reaction: Reduction half reaction:

31. 5.4 Oxidation and ReductionA. General Features Zn2+ + Cu Zn + Cu2+ oxidized reduced A compound that is reduced while causing another compound to be oxidized is called an oxidizing agent. • Cu2+ acts as an oxidizing agent because it causes Zn to lose electrons and become oxidized.

32. 5.4 Oxidation and ReductionA. General Features Zn2+ + Cu Zn + Cu2+ oxidized reduced A compound that is oxidized while causing another compound to be reduced is called a reducing agent. • Zn acts as a reducing agent because it causes Cu2+ to gain electrons and become reduced.

33. 5.4 Oxidation and ReductionA. General Features

34. 5.4 Oxidation and ReductionB. Examples of Oxidation–Reduction Reactions Iron Rusting O gains e– and is reduced. 4 Fe(s) + 3 O2(g) 2 Fe2O3(s) neutral Fe neutral O Fe3+ O2– Fe loses e– and is oxidized.

35. 5.4 Oxidation and ReductionB. Examples of Oxidation–Reduction Reactions Zn + 2 MnO2 ZnO + Mn2O3

36. Zn + 2H+ Zn2+ + H2 Fe3+ + Al  Al3+ + Fe

37. I- + Br2 I2 + Br- AgBr  Ag + Br2

38. 5.4 Oxidation and ReductionB. Examples of Oxidation–Reduction Reactions Oxidation results in the: Reduction results in the: • Gain of oxygen atoms • Loss of hydrogen atoms • Loss of oxygen atoms • Gain of hydrogen atoms

39. 5.5 The Mole and Avogadro’s Number A mole is a quantity that contains 6.02 x 1023 items. • 1 mole of C atoms = 6.02 x 1023 C atoms • 1 mole of H2O molecules = 6.02 x 1023 H2O molecules • 1 mole of Vitamin C molecules = 6.02 x 1023 Vitamin C molecules The number 6.02 x 1023 is Avogadro’s number.

40. How many items do 1 mol of the following contain: • Baseballs • Bicycles • Cheerios • CH4 molecules

41. 5.5 The Mole and Avogadro’s Number It can be used as a conversion factor to relate the number of moles of a substance to the number of atoms or molecules: 1 mol 6.02 x 1023 atoms 6.02 x 1023 atoms 1 mol or 1 mol 6.02 x 1023 molecules 6.02 x 1023 molecules 1 mol or

42. 5.5 The Mole and Avogadro’s Number Sample Problem 5.5 How many molecules are contained in 5.0 moles of carbon dioxide (CO2)? Identify the original quantity and the desired quantity. Step [1]

43. 5.5 The Mole and Avogadro’s Number Step [2] Write out the conversion factors. Step [3] Set up and solve the problem.

44. How many C atoms are there in the following: • 2.0 mol • 6.0 mol • 0.5 mol • 25.0 mol

45. How many molecules are contained in each of the following number of moles • 2.5mol of penicillin • 0.25 mol of NH3 • 0.4 mol of Sugar • 55.3 mol of Acetaminophen

46. 5.6 Mass to Mole Conversions • The formula weight is the sum of the atomic weights of all the atoms in a compound, reported in atomic mass units (amu). HOW TO Calculate the Formula Weight of a Compound Example Calculate the formula weight for FeSO4. Step [1] Write the correct formula and determine the number of atoms of each element from the subscripts.

47. 5.6 Mass to Mole Conversions HOW TO Calculate the Formula Weight of a Compound Multiply the number of atoms of each element by the atomic weight and add the results. Step [2]

48. 5.6 Mass to Mole ConversionsA. Molar Mass • The molar mass is the mass of one mole of any substance, reported in grams per mole (g/mol). • The value of the molar mass of a compound in grams equals the value of its formula weight in amu.

49. 5.6 Mass to Mole ConversionsB. Relating Grams to Moles • The molar mass relates the number of moles to the number of grams of a substance. • In this way, molar mass can be used as a conversion factor. • The molar mass of H2O is 18.0 g/mol, the conversion factor can be written:

50. 5.6 Mass to Mole ConversionsB. Relating Grams to Moles Sample Problem 5.9 How many moles are present in 100. g of aspirin (C9H8O4)? Step [1] Calculate the molar mass.