Chapter 10 Chemical Reactions

2 Homework for Chap 10 Read p 273 – 286; Applying the Concepts # 1 – 37, 39 – 42, 44 – 47,

3 Molecular formula shows the actual number of atoms of each element in the smallest unit of a substance Empirical formula shows the simplest whole-number ratio of the atoms in a substance H2OH2O H2OH2O molecularempirical C 6 H 12 O 6 CH 2 O O3O3 O N2H4N2H4 NH 2 Chemical Formulas

Fig Several ways to express common molecules

3 ways of representing the reaction of H 2 with O 2 to form H 2 O Chemical reaction ≡ process in which one or more substances is changed into one or more new substances Chemical equation ≡ use of chemical symbols to show what happens during a chemical reaction reactantsproducts

Fig The Combustion of Charcoal C + O 2 → CO 2 “Carbon reacts with oxygen to yield carbon dioxide”

Fig The meaning of subscripts and coefficients

Fig Illustration of the Law of Conservation of Mass

Fig Hydrocarbons and Carbohydrates C 8 H 18 C3H8C3H8 C 12 H 22 O 11

10 Types of Chemical Reactions 1)Oxidation-Reduction (Redox) 2) Combination 3) Decomposition 4) Replacement 5) Ion Exchange

Oxidation-Reduction Reactions (electron transfer reactions) 2 Mg (s) + O 2 (g) 2 MgO (s) Mg is the reducing agent (supplies electrons and is oxidized) O 2 is the oxidizing agent (takes electrons and is reduced) Oxidation – an atom loses electrons Reduction – an atom gains electrons Mg 2+ O 2-

Fig Example of an oxidizing agent (“chlorine”) Others: 1) Bleach 2) Hydrogen peroxide 3) Oxygen 4) Ultraviolet light

13 Types of Chemical Reactions 1)Oxidation-Reduction (Redox) 2) Combination 3) Decomposition 4) Replacement 5) Ion Exchange

Fig Iron combines with oxygen to form rust (iron oxide) 4 Fe (s) + 3 O 2 (g) 2 Fe 2 O 3 (s)

Hydrogen combines with oxygen to form water (dihydrogen monoxide)

16 Types of Chemical Reactions 1)Oxidation-Reduction (Redox) 2) Combination 3) Decomposition 4) Replacement 5) Ion Exchange

F IG D ECOMPOSITION OF M ERCURY O XIDE 2 HgO (s) → 2 Hg (l) + O 2 (g) heat

Decomposition of Hydrogen Peroxide 2 H 2 O 2 (l) → 2 H 2 O (l) + O 2 (g) (Demo)

19 Types of Chemical Reactions 1)Oxidation-Reduction (Redox) 2) Combination 3) Decomposition 4) Replacement 5) Ion Exchange

Fig Replacement reaction between aluminum metal and the blue copper chloride solution 2 Al (s) 3 CuCl 2 (aq) → 2 AlCl 3 (aq) + 3 Cu (s) CuCl 2 Cu Al AlCl 3

Replacement reactions take place when Replacement reactions take place when a more active metal gives up electrons to a less active metal. How do we know if a replacement reaction How do we know if a replacement reaction will take place or not occur? Refer to the activity series for common metals Refer to the activity series for common metals Fig 10.12, p 264 Fig 10.12, p 264

Fig The activity series for common metals

2 Na + 2H 2 O 2NaOH + H 2 ↑ Zn + 2HCl ZnCl 2 + H 2 ↑ Cu + HCl no reaction