Classifying Reactions

Classifying Reactions A guide

Think about the demonstrations you watched just now…  Which

reaction gave off heat?  Which one absorbed heat?

Any reaction that gives off heat is called an “exothermic” reaction Any reaction that absorbs heat is called an “endothermic” reaction

There are many different ways to classify reactions  We

will look at one way which splits all chemical reactions into 5 types  The types are: synthesis, decomposition, single displacement, double

displacement and combustion

But 1st, HOW TO WRITE A REACTION EQUATION What you start with

⇒

What you end with

Reactants

⇒

products

Synthesis Reactions  This

is when 2 substances combine to form another substance  General reaction: A + B ⇒ AB  Examples: Zn + S ⇒ ZnS  Nitrogen and hydrogen ⇒ ammonia

Decomposition Reactions  This

is the opposite of a synthesis reaction  One chemical is broken down into its components  General equation: AB ⇒ A + B  Examples: water ⇒hydrogen and oxygen  H2CO3 ⇒ H2O + CO2

Single Displacement Reactions  General

equation: A + BC ⇒

AB + C  Examples: H2O + K ⇒ KOH + H2 + hydrochloric acid ⇒ zinc chloride + hydrogen

 Zinc

Double Displacement Reactions  When

two substances “swap” or “trade” their components  General equation: AB + CD ⇒ AD + CB  General examples: acid + base ⇒ water + salt  HCl + NaOH ⇒ H2O + NaCl  Lead nitrate + potassium iodide ⇒ lead iodide + potassium nitrate

Combustion Reactions  Exothermic

reactions involving adding oxygen to substance(s)  Most of the time these reactions will involve molecules containing carbon and hydrogen  General equation: CxHy + O2⇒ CO2 + H2O methane + oxygen ⇒ carbon dioxide + water

 Example: