What is a Chemical Reaction? Definition of a Chemical Reaction
Define a Chemical Reaction: A chemical reaction involves a process in which substances (gas, solids or liquids) are mixed and then changed into different substances - they react to form something else. Chemical reactions are manifested by the disappearance of properties characteristic of the first substance and the appearance of new properties in the new substance or Compound. The substance (or substances) initially involved in chemical reactions are called reactants or reagents. Chemical reactions are described with chemical equations. Most chemical reactions are reversible.

Types of Chemical Reactions
A Chemical reaction  tends to involve the motion of electrons, leading to the formation and breaking of chemical bonds. There are several different types of chemical reactions.

• Combustion reactions: A combustion type of chemical reaction is when oxygen combines with another compound to form water and carbon dioxide. Combustion reactions always involve molecular oxygen O_2. When a substance burns, it is a combustion reaction. Combustion reactions are almost always exothermic meaning that they give off heat

• Combination reactions: A combination type of chemical reaction is when a substance combine with another substance

• Decomposition reactions: A decomposition type of chemical reaction is the opposite of a combination reaction - a complex molecule breaks down to make simpler ones

• Substitution or Single displacement Chemical Reactions: A Substitution or Single displacement type of chemical reaction is when one element trades places or is substituted from a compound by another element

• Double displacement reactions: A Double displacement type of chemical reaction is when the anions and cations of two different molecules switch places (exchange bonds or ions), forming two entirely different compounds

• Acid-base reactions:  An acid base type of chemical reaction is a special kind of double displacement reaction that takes place when an acid and base react with each other

Examples of a Chemical Reactions
Examples of a chemical reaction include burning, fermentation, tarnishing or rusting. Examples of different types of Chemical reactions are as follows:

• Combustion: An example of a combustion chemical reaction is when one methane molecule burns in the presence of two oxygen molecules to produce one carbon dioxide molecule and two water molecules

• Combination reaction: The combination of iron and sulfur which will form iron sulfide. Another example is the combination of barium metal and fluorine gas to form barium fluoride

• Decomposition reaction: An example of a decomposition chemical reaction is the electrolysis of water into oxygen and hydrogen gas. Another example is when mercury oxide is heated it will decompose into mercury metal and oxygen

• Substitution or Single displacement: An example of a Substitution or single displacement chemical reaction is when zinc combines with hydrochloric acid. In this example the zinc replaces the hydrogen

• Double displacement: An example of a double displacement chemical reaction is when the compounds of sodium chloride and silver nitrate switch places to form sodium nitrate and silver chloride

• Acid-base reaction: An example of an acid based chemical reaction is when hydrobromic acid and sodium hydroxide react with each other. Another example is when hydrocyanic acid and sodium hydroxide react with each other

The Rate of a Chemical Reaction
The rate of Chemical Reactions relates how fast or slow a chemical reaction takes place. The rate of chemical reaction can range from taking years or just seconds. For example, the combustion of butane in a fire can take seconds whereas the oxidization of iron in air can take years. There are several factors which can influence the rate of a chemical reaction. These factors include the following:

• Physical State: The physical state of a substance can effect the rate of chemical reaction - a solid moves much more slowly than a gas

• Temperature: Reaction rates for many substances double for every 10 degrees Celsius increase in temperature

• Pressure: The rate of reaction in gases increase with pressure

• Solvents: The properties of solvents can affect the chemical reaction rate

• Catalysts: The presence of a catalyst increases the reaction rate

• Surface Area: The rate of reaction increases according to the surface area

• Electromagnetic radiation and intensity of light generally will increase the rate of a chemical reaction

Examples of a Chemical Reactions
Examples of chemical reactions of various compounds formed by different elements can be found by referring to the following articles: