Unit 4 Part 3Chemical Reactions

Chemical ReactionsThe Importance of Chemical Reactions:

Many chemical reactions occur naturally, although some take place so slowly that we do not notice them.

Biochemical Reactions The natural chemical reactions that we

observe occurring in living things are known as biochemical reactions.

2 important chemical reactions are shown below: Respiration: C6H12O6 + 6O2 6CO2 +

6H2O + energy Photosynthesis: 12H2O + 6CO2 +

energy C6H12O6 + 6H2O + 6O2

Manufacture Important Chemicals Many important chemicals are created

through chemical reactions. Examples: Fertilizers, cement, plastics,

synthetic textiles, and pharmaceuticals.

Harmful Chemical ReactionsThere are also chemical reactions

that harm living organisms and harm the environment.

(See RAFT assignment)

Review Chemical Reactions: Indicator that a chemical change has occurred:

Other signs of a chemical change: Change in electrical conductivity Change in melting point or boiling point Change in density Change in taste

Types of Chemical ReactionsA reaction occurs when two or

more molecules interact and a chemical change occurs. A chemical change MUST occur in order for a chemical reaction to occur.

Chemical reactions start with the reactants and go to the products.

Synthesis/ Combination: A synthesis reaction is when two or

more simple compounds combine to form a more complicated one. These reactions come in the general form of:

A + B ---> AB

Synthesis/ Combination: One example of a synthesis reaction is

the combination of iron and sulfur to form iron (II) sulfide:

8 Fe + S8 --->

Decomposition: A decomposition reaction is the opposite

of a synthesis reaction - a complex molecule breaks down to make simpler ones. These reactions come in the general form:

AB ---> A + B

Decomposition: One example of a decomposition

reaction is the electrolysis of water to make oxygen and hydrogen gas:

2 H2O--->

Single displacement: This is when one element trades places

with another element in a compound. These reactions come in the general form of:

A + BC ---> AC + B

Single displacement: One example of a single displacement

reaction is when magnesium replaces hydrogen in water to make magnesium hydroxide and hydrogen gas:

Single displacement:The Activity Series:The activity series of an element is

used to determine whether or not a single displacement reaction will occur.

Single displacement:The Activity Series

lithium

These metals displace hydrogen from water

potassiumbariumcalciumsodiummagnesium

These metals displace hydrogen from acids

aluminumzincironnickeltinleadhydrogen  copper

These metals do not react with acids or pure water

mercurysilvergold

Each metal will displace any metal ion that appears below it in the series.

Single displacement: Examples:Cu(s) + FeSO4(aq)

Zn(s) + 2 HCl(aq)

2 Na(s) + 2 H2O(l)

Single displacement:

The Halogen Displacement Series

Each halogen willdisplace any halideion that appears below it

fluorine

chlorine

bromine

iodine

The Halogen Displacement Series

Single displacement: Examples: determine whether a reaction

will occur, if so, what are the products?Br2(aq) + 2 NaCl(aq) Zn(s) + NiCl2(aq) I2(aq) + 2 KF(aq) F2(aq) + 2 KI(aq) Cu(s) + 2 AgNO3(aq)

Double displacement: This is when the anions and cations of

two different molecules switch places, forming two entirely different compounds. These reactions are in the general form:

AB + CD ---> AD + CB

Double Displacement One example of a double displacement

reaction is the reaction of lead (II) nitrate with potassium iodide to form lead (II) iodide and potassium nitrate:

Double Displacement How can we predict when a double

displacement reaction will occur? Such reactions usually result in the formation of a precipitate, a gas, or water.

Acid Base This is a special kind of double displacement

reaction that takes place when an acid and base react with each other. The H+ ion in the acid reacts with the OH- ion in the base, causing the formation of water. Generally, the product of this reaction is some ionic salt and water:

HA + BOH ---> H2O + BA

Acid Base One example of an acid-base reaction is

the reaction of hydrobromic acid (HBr) with sodium hydroxide:

Funny Joke: The base is under a salt: NaCl

NaOH

Combustion: A combustion reaction is when oxygen

combines with another compound to form water and carbon dioxide. These reactions are exothermic, meaning they produce heat. An example of this kind of reaction is the burning of napthalene:

C10H8 + 12 O2 --->

Steps to determine types of reactions:Follow this series of questions. When you can answer "yes" to a question, then stop! 1)  Does your reaction have oxygen as one of its reactants and carbon dioxide and water as products? If yes, then it's a combustion reaction 2)  Does your reaction have two (or more) chemicals combining to form one chemical? If yes, then it's a synthesis reaction 3)  Does your reaction have one large molecule falling apart to make several small ones? If yes, then it's a decomposition reaction 4)  Does your reaction have any molecules that contain only one element? If yes, then it's a single displacement reaction 5)  Does your reaction have water as one of the products? If yes, then it's an acid-base reaction 6)  If you haven't answered "yes" to any of the questions above, then you've got a double displacement reaction

AssignmentSee types of reactions assignment (Pg 24)