TYPES OF CHEMICAL REACTIONS AND ENERGY IN REACTIONS

TYPES OF CHEMICAL REACTIONS

There are many types of chemical reactions They have been classified into five types Synthesis, Combustion Decomposition, Single

Replacement, and Double Replacement Each type of reaction follows a certain set of

rules

SYNTHESIS REACTIONS

A synthesis reaction is when two or more substances combine to form another substance

A general formula for a synthesis reaction is A + B -> AB

2Na + Cl2 ->2NaCl

DECOMPOSITION REACTION

SINGLE REPLACEMENT REACTION

Also called a single displacement reaction A single replacement reaction is when one

element replaces another in a reaction The general formula of a single replacement

reaction is A + BC -> AC + B 2Na + 2H2O--> 2NaOH + H2

DOUBLE REPLACEMENT REACTION Also called a double displacement reaction A double replacement is when the positive ion of

one compound replaces that of another to create two new compounds

A double replacement reaction takes place if a precipitate, water, or a gas forms when two ionic compounds in a solution are combined

A precipitate is an insouluble compound that comes out of a solution

The general fromula for a double replacement reaction is AB + CD -> AD + CB

AgNO3 + NaCl → AgCl + NaNO3

COMBUSTION REACTIONS

A combustion reaction occurs when a substance reacts with oxygen to produce energy in the form of heat and light

Combustion reactions also produce one or more products that contain the elements of the reactants

Many combustion reactions can also be classified as other types

2 H2 + O2 → 2 H2O(g) + heat

OXIDATION-REDUCTION REACTIONS Many reactions cause substances to gain or

lose electrons Oxidation describes the loss of electrons Reduction describes the gain of electrons Many reactions involving electron transfer

involve oxygen pulling electrons from metallic elements

The substance that gains electrons becomes more negative and and we say it is reduced

The substance that loses electrons becomes more positive and we say it is oxidized

Reduction always happens with oxidation, and is commonly called redox.

ENERGY EXCHANGE IN CHEMICAL REACTIONS

Chemical bonds are the source of energy in a chemical reaction

When bonds are broken this requires energy When new bonds are formed, energy is

released Combustion reactions require much less

energy to break the bonds than the energy released when the new bonds are formed

MORE ENERGY OUT

Chemical reactions that release energy are called exergonic reactions

In these reactions, less energy is required to break the bonds than is released

As a result of this, some form of energy is released, such as light or heat

When the energy given off by a reaction is primaraly heat, the reaction is called exothermic

Burning wood, exploding dynamite, and rusting metal are all exothermic reactions

Exothermic reactions provide most of the power used in homes and industry

MORE ENERGY IN

A recation that requires more energy to break bonds than is released is called endergonic

The energy absorbed can be in the form of light, heat, or electricity

When the energy needed for a reaction is in the form of heat, the reaction is called endothermic

Endothermic reactions can absorb enough heat to freeze water

Any form of cooking is usually an endothermic reaction, photosynthesis

CATALYSTS AND INHIBITORS

A catalyst is a substance that speeds up a chemical reaction without being permanently changed itself

Catalysts can be reused in another chemical reaction

Inhibitors are substances that are used to slow a chemical reaction