A chemical reaction is a process that leads to the chemical transformation of one set of chemical substances to another. Classically, chemical reactions encompass changes that only involve the positions of electrons in the forming and breaking of chemical bonds between atoms, with no change to the nuclei (no change to the elements present), and can often be described by a chemical equation. Nuclear chemistry is a sub-discipline of chemistry that involves the chemical reactions of unstable and radioactive elements where both electronic and nuclear changes can occur.
Types of Chemical Reactions
The vast number of chemical reactions can be classified in any number of ways. Under one scheme they can be categorized either as oxidation-reduction (electron transfer) reactions or non-oxidation-reduction reactions. Another completely different but common classification scheme recognizes four major reaction types:
(1) combination or synthesis reactions
(2) decomposition reactions
(3) substitution or single replacement reactions
(4) metathesis or double displacement reactions
The Four Major Types of Reactions are:
|Name||General Reaction Pattern|
|Combination or synthesis||A + B ----> AB|
|Decomposition||AB ----> A + B|
|Substitution or Single Replacement||A + BC ----> B + AC|
|Metathesis or Double Displacement||AB + CD ----> AD + CB|
Combination or Synthesis Reactions Two or more reactants unite to form a single product.
S + O2 ---------> SO2
sulphur oxygen sulphur dioxide
2 S + 3 O2 ---------> 2 SO3 sulphur oxygen sulphur trioxide 2 Fe + O2 ---------> 2 FeO iron oxygen iron (II) oxide
Decomposition Reactions A single reactant is decomposed or broken down into two or more products.
CaCO3 ----------> CaO + CO2
calcium carbonate calcium oxide carbon dioxide
2 H2O -----------> 2 H2 + O2 water hydrogen oxygen 2 KClO3 -----------> 2 KCl + 3 O2 potassium chlorate potassium chloride oxygen
Substitution or Single Replacement Reactions A single free element replaces or is substituted for one of the elements in a compound. The free element is more reactive than the one it replaces.
Zn + 2 HCl ----------> H2 + ZnCl2
zinc hydrochloric acid hydrogen zinc chloride
Cu + 2 AgNO3 -----------> 2 Ag + Cu(NO3)2 copper silver nitrate silver copper (II) nitrate H2 + 2 AgNO3 -----------> 2 Ag + 2 HNO3 hydrogen silver nitrate silver nitric acid 2 Na + 2 H2O -----------> 2 NaOH + H2 sodium water sodium hydroxide hydrogen
Metathesis or Double Displacement Reactions This reaction type can be viewed as an “exchange of partners.” For ionic compounds, the positive ion in the first compound combines with the negative ion in the second compound, and the positive ion in the second compound combines with the negative ion in the first compound.
HCl + NaOH -----------> NaCl + HOH
hydrochloric sodium sodium water
acid hydroxide chloride
BaCl2 + 2 AgNO3 ----------> 2 AgCl + Ba(NO3)2 barium silver silver barium chloride nitrate chloride nitrate (precipitate) CaCO3 + 2 HCl -----------> CaCl2 + H2CO3 calcium hydrochloric calcium carbonic carbonate acid chloride acid
An acid-base reaction is a type of double displacement reaction that occurs between an acid and a base. The H+ ion in the acid reacts with the OH- ion in the base to form water and an ionic salt:
HA + BOH → H2O + BA
The reaction between hydrobromic acid (HBr) and sodium hydroxide is an example of an acid-base reaction:
HBr + NaOH → NaBr + H2O
Common Types of Chemical Reactions
Several general types of chemical reactions can occur based on what happens when going from reactants to products. The more common types of chemical reactions are as follows:
- Single displacement
- Double displacement
Combination chemical reactions
In combination reactions, two or more reactants form one product. The reaction of sodium and chlorine to form sodium chloride,
and the burning of coal (carbon) to give carbon dioxide,
are examples of combination reactions.
Decomposition chemical reactions
Decomposition reactions are really the opposite of combination reactions. In decomposition reactions, a single compound breaks down into two or simpler substances (elements and/or compounds).
The decomposition of water into hydrogen and oxygen gases,
and the decomposition of hydrogen peroxide to form oxygen gas and water,
are examples of decomposition reactions.
Single displacement chemical reactions
In single displacement reactions, a more active element displaces (kicks out) another less active element from a compound. For example, if you put a piece of zinc metal into a copper(II) sulfate solution, the zinc displaces the copper, as shown in this equation:
The notation (aq) indicates that the compound is dissolved in water — in an aq aqueous solution. Because zinc replaces copper in this case, it’s said to be more active. If you place a piece of copper in a zinc sulfate solution, nothing will happen.
The Activity Series of Some Common Metals
Alkali and alkaline earth metals
Double displacement chemical reactions
In single displacement reactions, only one chemical species is displaced. In double displacement reactions , or metathesis reactions , two species (normally ions) are displaced. Most of the time, reactions of this type occur in a solution, and either an insoluble solid (precipitation reactions) or water (neutralization reactions) will be formed.
If you mix a solution of potassium chloride and a solution of silver nitrate, a white insoluble solid is formed in the resulting solution. The formation of an insoluble solid in a solution is called precipitation.
Here is the molecular equation for this double-displacement reaction:
The white insoluble solid that’s formed is silver chloride.
The other type of double displacement reaction is the reaction between an acid and a base. This double-displacement reaction, called a neutralization reaction, forms water. Take a look at the mixing solutions of sulfuric acid (auto battery acid) and sodium hydroxide (lye).
Here is the molecular equation for this reaction:
Combustion chemical reactions
Combustion reactions occur when a compound, usually one containing carbon, combines with the oxygen gas in the air. This process is commonly called burning. Heat is the most-useful product of most combustion reactions.
Here’s the equation that represents the burning of propane:
Propane belongs to a class of compounds called hydrocarbons , compounds composed only of carbon and hydrogen. The product of this reaction is heat.
Combustion reactions are also a type of redox reaction.
Redox chemical reactions
Redox reactions , or reduction-oxidation reactions , are reactions in which electrons are exchanged:
In an isomerization reaction, the structural arrangement of a compound is changed but its net atomic composition remains the same.
A hydrolysis reaction involves water. The general form for a hydrolysis reaction is:
X-(aq) + H2O(l) ↔ HX(aq) + OH-(aq)
Frequently Asked Questions (FAQs)
1. What are the 5 types of chemical reactions?
5 types of chemical reactions are:
- Single Displacement.
- Double Displacement.
2. What type of simple chemical reactions occurs in fireworks?
The simple chemical reactions that occur in fireworks are combustion and oxidation.
Combustion and Oxidation
Combustion reactions typically require the addition of heat and include oxygen as a reactant. Oxidation involves losing of electrons by an element (or usually gaining oxygen by a chemical). It should be noted that oxidation is always accompanied by reduction which is the gaining of electrons by an element.
3. Which list includes three types of chemical reactions?
Three types of chemical reactions are:
(1) condensation, double replacement, and sublimation
(2) condensation, solidification, and synthesis
(3) decomposition, double replacement, and synthesis
4. What type of chemical reaction absorbs thermal energy?
Endothermic reactions, on the other hand, absorb heat and/or light from their surroundings. For example, decomposition reactions are usually endothermic. In endothermic reactions, the products have more enthalpy than the reactants. Thus, an endothermic reaction is said to have a positive enthalpy of reaction. This means that the energy required to break the bonds in the reactants is more than the energy released when new bonds form in the products; in other words, the reaction requires energy to proceed.
The decomposition of water into hydrogen and oxygen when water is heated to over 2000 degrees Celsius, a small fraction will decompose into hydrogen and oxygen. Significant heat energy is needed for this reaction to proceed, so the reaction is endothermic.
5. What is a type of protein that speeds up chemical reactions?
Enzymes are proteins that catalyze, or ‘speed up’, chemical reactions.
‘Speeding up’, also known as catalysis, is the process by which the rate of a chemical reaction increases. Proteins, which are like the laborers of the cell, which catalyze chemical reactions are called enzymes. One example of an enzyme is glucosidase, which takes maltose, a disaccharide, and splits it up into two monosaccharides (glucose) much more quickly than a molecule of maltose could split into two glucose molecules independently.
6. How to identify types of chemical reactions?
The following are indicators of chemical changes:
- Change in Temperature.
- Change in Color.
- Noticeable Odor (after the reaction has begun)
- Formation of a Precipitate.
- Formation of Bubbles.