Chemical Reactions Chapter 13

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

Reducing agents (be oxidized) Oxidizing agents (be reduced)

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

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

Iron can be protected from rusting by coating the iron with zinc: “galvanized” 2 Zn (s) + O 2 (g) 2 ZnO (s)

Hydrogen combines with oxygen to form water (dihydrogen monoxide) Fast reaction

Chemical Kinetics Kinetics – how fast does a reaction proceed? Reaction rate - the change in the concentration of a reactant or a product with time (M/s). What determines the rate of a reaction? Factors that Affect Reaction Rate Concentration (increase frequency of collisions) Concentration (increase frequency of collisions) Temperature (increases force of collisions) Temperature (increases force of collisions) Adding a Catalyst (reduces activation energy) Adding a Catalyst (reduces activation energy)

Fig Relative orientation of reacting molecules KI KI

Adding a Catalyst uncatalyzedcatalyzed Fig Catalysts in the human body are called enzymes.

Catalytic Converters CO + Unburned Hydrocarbons + O 2 CO 2 + H 2 O catalytic converter 2NO + 2NO 2 2N 2 + 3O 2 catalytic converter Technology pg 286 Platinum, palladium, rhodium

Exothermic process - gives off heat – transfers thermal energy from the system to the surroundings. 2H 2 (l) + O 2 (l) 2H 2 O (l) + energy H 2 O (g) H 2 O (l) + energy

Endothermic process - heat has to be supplied to the system from the surroundings. energy + N 2 (g) + O 2 (g) → 2 NO (g) Energy + ammonium nitrate + water → solution of ammonium nitrate