Types of Chemical Reactions

Exothermic and Endothermic Chemical reactions involve changes in energy. All chemical reactions, regardless of what type, can be classified as exothermic or endothermic.

Exothermic and Endothermic Ex- out Therm- heat Release heat (and often light) to their surroundings Temperature goes up Happens when bonds are formed

Examples Burning Rusting

Exothermic and Endothermic Endo- in Therm- heat Absorbs heat from the surroundings Temperature goes down Happens when bonds are broken

Examples Instant cold pack Baking soda + vinegar Photosynthesis

Synthesis Syn- together Two or more reactants combine to form one product A + B  AB

Often release heat and light (exothermic) Synthesis Often release heat and light (exothermic)

Na + Cl  NaCl Sodium + Chlorine  Sodium Chloride Synthesis Na + Cl  NaCl Sodium + Chlorine  Sodium Chloride 2 reactants 1 product

Other examples: C + O2  CO2 2CaO + H2O  2Ca(OH)2 2CO + O2  2CO2 Synthesis Other examples: C + O2  CO2 2CaO + H2O  2Ca(OH)2 2CO + O2  2CO2 2 reactants 1 product

One reactant is broken down into two or more products Decomposition De-remove; undo One reactant is broken down into two or more products (Opposite of a synthesis reaction) AB  A + B

Decomposition These reactions usually have to absorb heat, light, or electricity to break down the compound. Heat Heat

2H2O2  2H2O + O2 Hydrogen Peroxide  Water + Oxygen Decomposition 2H2O2  2H2O + O2 Hydrogen Peroxide  Water + Oxygen 1 reactant 2 products

Other examples: H2CO3  H2O + CO2 2H2O  2H2 + O2 2Al2O3  4Al + 3O2 Decomposition Other examples: H2CO3  H2O + CO2 2H2O  2H2 + O2 2Al2O3  4Al + 3O2 1 reactant 2 products

Single Replacement A single element reacts with a compound and takes the place (replaces) of one of the elements in that compound. The result is a new compound and a new element. A + BC  B + AC

Single Replacement Usually, similar elements will “replace” each other. Metals replace metals, nonmetals replace nonmetals, etc.

Zn + CuCl2  ZnCl2 + Cu Single Replacement Zinc + Copper Chloride  Zinc Chloride + Copper Zinc replaces copper to bond with chlorine Zinc and Copper are both metals

Single Replacement Other examples: Br2 + 2KI  2KBr + I2 Mg + CuSO4  Cu + MgSO4 Bromine replaces Iodine Magnesium replaces Copper

Double Replacement A reaction between two compounds where one element from each compound switches places. It is a double replacement because the two elements “replace” each other in the reaction. ds AB + CD  CB + AD

Double Replacement On the reactant side are two compounds and on the product side are two NEW compounds. AB + CD  CB + AD

2 compounds  2 new, different compounds Double Replacement BaCl2 + MgSO4  MgCl2 + BaSO4 Barium Chloride + Magnesium Sulfate  Magnesium Chloride + Barium Sulfate 2 compounds  2 new, different compounds

Double Replacement Other examples: Na2S + 2HCl  2NaCl + H2S KBr + AgNO3  KNO3 AgBr Sodium and Hydrogen switch places Potassium and Silver switch places

Combustion Combustio- to burn A fuel is combined with oxygen to (usually) produce carbon dioxide and water. Fuel + O2  CO2 + H2O

Combustion Combustion reactions are also called burning. Usually occurs at high temperatures. Releases amounts of heat and light

Combustion Burning of acetylene (used in welding torches) 2C2H2 + 5O2  4CO2 + 2H2O Oxygen Carbon Dioxide Fuel Water

Combustion Burning Methane CH4 + 2O2  CO2 + 2H2O Other examples: Burning Methane CH4 + 2O2  CO2 + 2H2O Burning Coal (pure carbon) C + O2  CO2 Burning Rocket Fuel (pure hydrogen) 2H2 + O2  2H2O

Other Types Oxidation: Reactions where an element or compound loses electrons because of an oxidizing agent (often Oxygen) Example: Iron rusting, an apple turning brown

NaHCO3 + HCl  NaCl + H2O + CO2 Other Types Acid-Base (Neutralization): An acid and a base react to form water and a salt. Example: Alka seltzer or Tums are taken to neutralize stomach acid NaHCO3 + HCl  NaCl + H2O + CO2