Chemical Reactions Reaction Types

A physical change involves a change in shape or a change in state of a substance. H H O H H O H H O

A chemical change is when new substances with new properties are formed - chemical reaction. There are 5 indicators of a chemical reaction: 1.A change in colour 2.A change in smell (odor) 3. Fizzing or bubbling (releasing gas)

4. A change in energy (light, heat, sound…) a. The container feels warmer, heat is released. We call this an exothermic change. (exo = out, therm = heat) b. The container feels cooler, heat is absorbed. We call this an endothermic change. (endo = in, therm = heat)

5. When two clear liquids are mixed, a solid forms or the mixture goes cloudy. This is called precipitate formation.

In nature there are millions of possible chemical reactions. Chemists have discovered that many reactions are similar. Once the chemist knows the type of reaction, then the products of the reaction can be predicted. So, the chemists have classified the reactions.

 Synthesis reactions  Decomposition reactions  Single replacement reactions  Double replacement reactions  Combustion reactions Key Words

Synthesis Reactions (Combination): 2 or more substances react to form a single substance. A + B  C S O S OO + O

Na + S Na 2 S H 2 + O 2 H 2 O K + Cl 2 KCl Fe + O 2 Fe 2 O

Decomposition Reactions: A single compound splits apart, into two or more simpler compounds. C  A + B S O S OO + O

MgCl 2 Mg + Cl 2 CO 2 CO + O 2 Al 2 S 3 Al + S

Single Replacement Reactions: One element replaces another element in a compound. More active elements replace less active elements. A + BC  AC + B A B + C

Cu + AgI Ag + CuI 2 I 2 + CuCl Cl 2 + CuI Al + ZnBr 2 Zn + AlBr 3 Ba + K(NO 3 ) K + Ba(NO 3 )

Double Replacement Reactions: 2 compounds split and exchange positive ions AB + CD  AD + BC

BaF 2 + LiBrBaBr 2 + LiF HCl + AlBr 3 HBr + AlCl 3 BeF 2 + Na 2 O BeO + NaF

Combustion Reactions: Oxygen reacts with a carbon compound to produce water, carbon dioxide and heat. C x H y + O 2  CO 2 + H 2 O

C 7 H 6 O + O 2 CO 2 + H 2 O C 3 H 8 + O 2 CO 2 + H 2 O CH 4 + O 2 CO 2 + H 2 O

Synthesis /combinationA + B  C DecompositionC  A + B Single replacementA + BC  B + AC Double replacement AC + BD  AD + BC Combustion C x H y + O 2  CO 2 + O 2