Reaction Type Notes

Most chemical reactions can be categorized into one of five types. You can usually identify the reaction type by looking at the reactants. Once the type of reaction is identified, we can predict the products

Types of Chemical Reactions Chemists classify reactions in order to organize the many types. A synthesis reaction is a reaction in which two or more substances react to produce a single product.synthesis reaction General form: A + B  AB or A + BC  ABC or AB + CD  ABCD

Types of Chemical Reactions (cont.) When two elements react, the reaction is always a synthesis reaction.

Reaction Type Notes Example: 2 H 2 + O 2  2 H 2 O

Reaction Type Notes Synthesis To predict the products: for binary compounds, put elements together and balance the charges. Otherwise, just combine. These reactions generally happen spontaneously, and are generally exothermic (release energy).

Types of Chemical Reactions (cont.) In a combustion reaction, oxygen combines with a substance and releases energy in the form of heat and light.combustion reaction Heated hydrogen reacts with oxygen to produce heat and water in a combustion reaction. This is also a synthesis reaction.

Reaction Type Notes Hydrocarbon Combustion—Involves a specific case of combustion in which a hydrocarbon (a substance containing carbon and hydrogen) reacts with oxygen to form carbon dioxide and water General form: C x H y + O 2  CO 2 + H 2 O

Reaction Type Notes Example: 2C 2 H 6 + 7O 2  4CO 2 + 6H 2 O

Reaction Type Notes Hydrocarbon Combustion To predict products: At least Carbon Dioxide and water. Always exothermic, but often requires a large activation energy, leading it to occur spontaneously

Decomposition Reactions A decomposition reaction is one in which a single compound breaks down into two or more elements or new compounds.decomposition reaction Decomposition reactions often require an energy source, such as heat, light, or electricity, to occur. General form: AB  A + B

Reaction Type Notes Example: 2H 2 O 2  2 H 2 O + O 2 (it needs a catalyst—Potassium Iodide)

Reaction Type Notes Decomposition To predict the products: Binary compounds separate into their two elements You will be given a handout to predict others Generally not spontaneous, and generally endothermic

Replacement Reactions A reaction in which the atoms of one element replace the atoms of another element in a compound is called a single replacement reaction.single replacement reaction A + BX → AX + B

Replacement Reactions (cont.) A metal will not always replace a metal in a compound dissolved in water because of differing reactivities. An activity series can be used to predict if reactions will occur.

Replacement Reactions (cont.) Halogens frequently replace other halogens in replacement reactions. Halogens also have different reactivities and do not always replace each other.

Reaction Type Notes Example: 2 Na + 2 H(OH)  2 Na(OH)+ H 2

Reaction Type Notes Single displacement To predict the products: The element switches places with the element of similar charge within the compound. If the element is more reactive then the one it attempts to replace, then the reaction will be spontaneous and exothermic. Otherwise, it will not be spontaneous and will be endothermic (require the input of energy).

Reaction Types Activity Series: Most Active Cations  Least Active Lithium Rubidium Potassium Barium Calcium Sodium Hydrogen (in water) Magnesium Aluminum Manganese Zinc Chromium Iron Nickel Tin Lead Hydrogen (in acids) Copper Mercury Silver Platinum Gold *Red not included in book values

Reaction Type Notes Activity Series: Most Active Anions  Least Active Fluorine Oxygen Chlorine Nitrogen Bromine Iodine Sulfur Selenium Astatine Phosphorus Tellurium Arsenic Polonium *Red not included in book values

Replacement Reactions (cont.) Double replacement reactions occur when ions exchange between two compounds.Double replacement reactions This figure shows a generic double replacement equation.

Reaction Type Notes Double displacement To predict the products: Like charged particles switch places Both compounds are initially stable and so reactions will usually not be spontaneous as solids. If compounds can be dissolved and dissociated (broken apart) then reaction will usually occur spontaneously to some degree, but not be highly exothermic

Replacement Reactions (cont.) This table shows the steps to write double replacement reactions.

Replacement Reactions (cont.) A solid product produced during a chemical reaction in a solution is called a precipitate. precipitate All double replacement reactions produce either water, a precipitate, or a gas.

Example: 2 NaI (aq) + Pb(NO 3 ) 2 (aq)  PbI 2 (s) + 2NaNO 3 (aq)

Reaction Type Notes Most reactions which do not appear to fit any of these five patterns are usually a combination of two or more of them happening simultaneously

Replacement Reactions (cont.) This table summarizes different ways to predict the products of a chemical reaction.