ScienceSuperSchool.com
Science Past, Present and Future
   Home      Chemical Reaction Types and Kinds – Concise Review with Examples Explanations
Chemical Reaction Types and Kinds – Concise Review with Examples Explanations
© Donald Reinhardt, November 4, 2013
The world of chemistry is exciting and interesting. Elements and the atoms of those elements are the building blocks of our universe and the physical worlds around us. Chemistry helps us understand how atoms of various elements act and interact. Here you will see and understand the basic types of chemical reactions which make, form and drive the chemical world.
 
 Chemical Reactions - Basic Facts, Information and Key Concepts
A chemical reaction begins with the interactions of atoms – the basic, fundamental and whole parts of elements.
Atoms are the smallest units of an element that have all the properties of that element.

Atoms can react and interact with one another to form compounds and these compounds can interact with other compounds or atoms.

Compounds are the products of chemical reactions formed from the interaction of atoms and molecules of various compounds.

Atoms or compounds which interact with one another in a chemical reaction are called reactants.

The result of a chemical reaction is the product or products.

Virtual experiment: Imagine here a piece of coal which contains the element carbon. Now, imagine, as is commonly the case, air with oxygen gas surrounding the coal. The carbon and oxygen are potential reactants, which when energy in the form of heat/flame is applied, can ignite. When the coal interacts chemically with oxygen the coal burns or oxidizes to produce light, heat and the product CO2.

C + O2 -------=à       CO2 +heat + light

Reactants ---=>       Products

Reaction Diagram above: Reactants of carbon and oxygen are ignited and burn to produce CO2, heat and light energy.

Types, Kinds, Classes of Chemical Reactions

1. Synthesis – a direct combination of two or more atoms of elements to form a compound. 

Virtual experiment 1:  Fe (iron filings) + Sulfur – –>        FeS (iron sulfide)

Virtual experiment 2:  O2 (oxygen gas) + H2 (gas) ––>   H2O (water)

The balanced equation for the above reaction is: O2 + 2H2 –> 2H2O

2. Decomposition – the breakdown of a compound into various elemental or atomic components. Compounds that are exposed to light, heat, or are simply regularly unstable, tend to decompose.

Virtual experiment 1: 2H2O2 (hydrogen peroxide) ---heat, light–> 2H2O and O2 (water and oxygen)

Virtual experiment 2: 2H2O (exposed to electric current = electrolysis) –> 2H2 + O2

3.  Combustion – the reaction a compound or an element with oxygen that causes it to burn and typically produce light and heat.

Virtual Experiment 1:   C (Coal as carbon) + O2 (oxygen gas) –-> CO2 + heat + light

Virtual experiment 2: CH4 (methane) or  propane (C3H8)+ O2 –> CO2 and H2O + heat + light

4. Single displacement or substitution – one atom of an element displaces or removes another atom and reacts with the atom of the remaining element.

 Example 1: Mg + 2HCl –> MgCl2 + H2   (Magnesium displaces the hydrogen atom to form magnesium chloride and hydrogen gas)

Example 2: Na + HOH –> NaOH + H2    (Sodium reacts with water, displaces the hydrogen to produce a strong base, sodium hydroxide and hydrogen gas).

5. Double displacement or substitution – here we find that there are two reciprocal substitution and exchanges between two compounds as in a classic acid and base reaction illustrated below.

NaOH + HCl –> NaCl + HOH  (sodium hydroxide, a base + hydrochloric acid, an acid, yields sodium chloride, table salt + water)
Exothermic and Endothemic Reactions
Some reactions generate heat energy when they occur – these are exothermic reactions. Exothermic reactions reactions always emit heat as they occur. 
Those reactions that require a constant input of energy to drive them are endothermic reactions (e.g., electrolytic breakdown of water).
At this point it is good to remember this fact:  The actual or potential heat energy of exothermic reactions may or can be used to drive or make possible endothermic reactions.This makes sense doesn't it?
Endothermic reactions cannot be used to drive other endothermic reactions – that, too, should be logical and clear.
Potential Energy and Kinetic Energy 
It is good to remember that there is energy stored in the bonds of compounds. This is the potential or stored energy. This energy can be released when a compound is activated. The energy that is released is typically in the form of heat or light or both.
 The amount of energy released can be determined for any given weight of a compound. Sugar, for example, when burned will generate 686,000 calories (686 kCal) for each mole of its total gram molecular weight of 180 grams.
Factors that Influence the Rate of Chemical Reactions
A few factors are very important which influence the rate or activity of chemical reactions. These factors include:
1. temperature – chemical reactions speed up when the temperature is raised. The higher the temperature, the speedier the reaction. In many cases reactions increase by a factor of two (2X) for each 10 degree C rise in temperature.
2. concentration of the reactants – Usually, the more concentrated the reactants, then the faster the reaction. Reactants are more likely to meet and collide with one another and then react. 
3. pressure of the system –The actual pressure exerted over a reaction vessel is important for gasses or liquids. The higher pressure keeps reactants closer together. Two gasses like H2 and O2 exposed to increased pressure will react faster.
Reversible Reactions and Reactions in Equilibrium
Reactions typically proceed from the reactant side to the product side of the equation. Eventually, if the products of the reaction are removed, preciptated, used up, or the reactants are used up –the reaction stops. However, sometimes the reaction can reverse itself and proceed back from product to reactant at least in part. A back and forth movement between the left and the right sides of the equation or chemical reaction means that an equilibrium has been reached. This equilibrium is common in certain types of reactions. Consider the hexose isomers glucose and fructose.
Example:
glucose  –-----> fructose
 glucose <------   fructose
 
 
 
 
Diagram of Photoelectric cell (PEC). The chemical decomposition reaction is producing oxygen and hydrogen gas from the breakdown of water. The energy that drives the reaction is provided by light. Photo Credit: Lawrence Berkeley National Laboratory, U.S.
 
Check out these chemical fun reactions and experiments:

http://imaginationstationtoledo.org/content/2011/04/how-to-make-a-naked-egg/