Chapter 5 Chemical Reactions The Nature of Reactions Types of Reactions Oxidation-Reduction Reactions Balancing Chemical Equations Rates of change

Chemical Reactions Change Substances Production of gas and change in color are signs of chemical reactions Chemical reactions rearrange atoms –Reactant is a substance that undergoes a chemical change. –Product is a substance that is the result of a chemical change.

Energy and Reactions Energy must be added to break bonds Forming bonds releases energy Energy is conserved in chemical reactions –Chemical Energy is stored energy within atoms and molecules that can be released when a substance reacts

Reactions that release energy are exothermic. –Exothermic reactions is a reaction that transfers energy from the reactants to the surroundings usually as heat. Energy and Reactions

Reactions that absorb energy are endothermic. –Endothermic reactions are those which energy is transferred to the reactants usually as heat from the surroundings Energy and Reactions

Type of Reactions Chemical reactions are classified into four general types Combination (Synthesis) Decomposition Single Replacement (Displacement) Double Replacement (Displacement) Play

Combination (Synthesis) Two or more elements or simple compounds combine to form (synthesize) one product A + B AB 2Mg + O 2 2MgO 2Na + Cl 2 2NaCl SO 3 + H 2 O H 2 SO 4

Decomposition One substance is broken down (split) into two or more simpler substances. ABA + B 2HgO2Hg + O 2 2KClO 3 2KCl + 3 O 2 Electrolysis is the decomposition of a compound by an electric current.

Checking Your Understanding 1 Classify the following reactions as 1) combination or 2) decomposition: ___A. H 2 + Br 2 2HBr ___B. Al 2 (CO 3 ) 3 Al 2 O 3 + 3CO 2 ___C. 4 Al + 3C Al 4 C 3

Classify the following reactions as 1) combination or 2) decomposition: _1_A. H 2 + Br 2 2HBr _2_B. Al 2 (CO 3 ) 3 Al 2 O 3 + 3CO 2 _1_C. 4 Al + 3C Al 4 C 3 Solution CYU 1

Single Replacement One element takes the place of an element in a reacting compound. A + BC AB + C Zn + 2HCl ZnCl 2 + H 2 Fe + CuSO 4 FeSO 4 +Cu

Double Replacement Two elements in reactants take the place of each other AB + CD AD + CB AgNO 3 + NaCl AgCl+NaNO 3 ZnS + 2HCl ZnCl 2 +H 2 S

Classify the following reactions as 1) single replacement 2) double replacement __A. 2Al + 3H 2 SO 4 Al 2 (SO 4 ) 3 + 3H 2 __B. Na 2 SO 4 + 2AgNO 3 Ag 2 SO 4 +2NaNO 3 __C. 3C + Fe 2 O 3 2Fe + 3CO Checking Your Understanding 2

CYU Solution 2 Classify the following reactions as 1) single replacement 2) double replacement 1_ A. 2Al + 3H 2 SO 4 Al 2 (SO 4 ) 3 + 3H 2 2_B. Na 2 SO 4 + 2AgNO 3 Ag 2 SO 4 +2NaNO 3 1_C. 3C + Fe 2 O 3 2Fe + 3CO

Combustion A reaction in which a compound (often carbon) reacts with oxygen C + O 2 CO 2 CH 4 + 2O 2 CO 2 + 2H 2 O C 3 H 8 + 5O 2 3CO 2 + 4H 2 O C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 O

Redox till 19:55 First! Oxidation and Reduction  Reactions that involve a loss or gain of electrons  Occurs in many of the 4 types of reactions and combustion  Important in food metabolism, batteries, rusting of metals  Nye part 1 Nye part 1

Requirements for Oxidization- Reduction Electrons are transferred Two processes occur Oxidation = Loss of electrons ZnZn e - (LEO) Reduction = Gain of electrons Cu e - Cu (GER)

Balanced Redox Equations Combine the oxidation and reduction reactions to make Loss of electrons = Gain of electrons Zn + Cu e - Zn e - + Cu Zn + Cu 2+ Zn 2+ + Cu

Gain/Loss of Hydrogen In organic and biological reactions oxidation = Loss of H reduction = Gain of H Nye part 2

Checking Your Understanding 3 Identify the following as an 1) oxidation or a 2 reduction process: __A. SnSn e- __B. Fe e - Fe 2+ __C. Cl 2 + 2e - 2Cl -

CYU Solution 3 Identify the following as an 1) oxidation or a reduction process: 1_ A. SnSn e- 2_ B. Fe e - Fe 2+ 2_ C. Cl 2 + 2e - 2Cl -

Checking Your Understanding 4 In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction Ag + + Cl - Ag + Cl A. Which reactant is oxidized 1) Ag + 2) Cl - 3) Ag B. Which reactant is reduced? 1) Ag + 2) Cl - 3) Cl

CYU Solution 4 In light-sensitive sunglasses, UV light initiates an oxidation-reduction reaction Ag + + Cl - Ag + Cl A. Which reactant is oxidized 2) Cl - Cl - Cl + e - B. Which reactant is reduced? 1) Ag + Ag + + e- Ag Nye Part 3 of 3