Type of Chemical Reactions •  Combination •  Decomposition •  Single Replacement •  Double Replacement •  Combustion

Reaction Types   There are five reaction types that have to be

identified and balanced 1.  Combination (or synthesis) 2.  Decomposition 3.  Single Replacement 4.  Double replacement 5.  Combustion

  In an experiment we would use multiple observation to identify reactions

Combination (Synthesis)  Two or more substances react to form a

single new substance  General equation: A + B à AB

  Example: Mg(s) + O2(g) à MgO(s)

 To determine products, reactant must be known (or vise versa)

Decomposition Reaction  A single compound breaks down into two

or more simpler products

 General equation: AB à A + B   Example: HgO(s) à Hg(l) + O2(g)

 Reverse of synthesis

Predicting Products   Synthesis:

  Combine the two elements together in a single chemical formula.

  Be sure to check charges (OXIDATION NUMBERS!!)  Cross-over when necessary (if it is IONIC!)

  Decomposition:   Separate the given compound into its elements.   Don’t forget about DIATOMIC elements!

 H2, N2, O2, F2, Cl2, Br2, I2

Examples (Balance them too!)  Mg + O2 à MgO  Questions to ask yourself:

1.  Are the charges balanced? Yes 2.  Are the metals ok? Yes 3.  Are the non-metals ok? No

  What do we need to add?

 Mg + O2 à MgO ______ Mg ______ Mg ______ O ______ O

Single Replacement  One element replaces a second element

in a compound

 General equation: A + BC à AC + B   Must conform to the activity series

 Ex: Cu(s) + AgNO3(aq) à Cu(NO3)2(aq) + Ag(s)

 Whether or not an element will replace another element depends on its REACTIVITY

 Copper (Cu) is more reactive than silver (Ag), therefore copper will replace silver in the reaction, causing silver to precipitate.

Single Replacement

Activity Series for Metals   A list that ranks metals

from most reactive to least reactive

  The activity series

answers the question, “Can one metal replace a metal inside a compound?”

  If the metal seeking to replace another metal is LESS reactive then the reaction will NOT happen

Examples of how activity series work

  Ca + AlCl3 à CaCl2 + Al   Calcium is more reactive than aluminum   Therefore, the reaction occurs

  2AlN + 3Mg à Mg3N2 + 2Al   Mg is more reactive than Al   Reaction will occur

  Cu + Na2O à NO REACTION   Copper is not more reactive than sodium   The reaction does not occur

Double Replacement   An exchange of positive ions between two

compounds   In order to take place, one of the new

compounds formed MUST leave the solution   Either as a gas or as a precipitate

  General equation: AB + CD à CB + AD   Ex: FeS + 2HCl à H2S + FeCl2

Predicting Products 1.  Swap the positive ions (Usually metals) 2.  Figure out the charges and criss cross to

get the formula

AlPO4 + FeI3 à AlI3(aq) + FePO4(s)

Examples Na2S(aq) + Cd(NO3)2(aq)à 2NaCN(aq) + H2SO4(aq)à 3NaOH(aq) + Fe(NO3)3(aq)à

3Ba(NO3)2(aq) +2H3PO4(aq)à (Barium Phosphate is a precipitate)

CdS(s) + 2NaNO3(aq)

2HCN(g) + Na2SO4(aq)

Fe(OH)3(s) + 3NaNO3(aq)

Ba3(PO4)2(s) + 6HNO3(aq)

Combustion   An element or a

compound reacts with oxygen (O2), often producing energy in the form of heat and light

  Hydrocarbons often combust

  Fossil fuels, good source of energy

  Products are often water and carbon dioxide (CO2)

Combustion Practice