What is a Chemical Reaction?
A chemical reaction is the process of converting one or more substances (reactants) into one or more new substances (products).
Reactants: These are the substances that start a chemical reaction or combine to start a chemical reaction. They are usually at the left hand side of the reaction before the arrow.
The arrow in a chemical reaction tells us, that a reaction has taken place and points towards the product of the reaction.
Products: These are the outcome of a successful chemical reaction, usually found at the right hand side of the arrow.
Types of Chemical Reactions
- Synthesis or Combination Reaction
- Decomposition Reaction
- Single Replacement or Displacement Reaction
- Double Replacement or Displacement Reaction
- Combustion Reaction
Synthesis or Combination Reaction
Synthesis or combination reaction is when two or more substances combine to form only one single product. See example in Fig. 1 below;
Decomposition Reaction
Decomposition reaction is when one large substance breaks down into two or more simple substances or its individual elements. See example in Fig. 2 below;
Single Replacement or Displacement Reactions
In single replacement or displacement reactions, an element replaces or displaces another element in a compound. For this to be possible, the element that will be replacing or displacing another must be more reactive or above in the reactivity series than the element to be replaced or displaced.
Reactivity Series of Metals
K – Potassium
Na – Sodium
Ba – Barium
Ca – Calcium
Mg – Magnessium
Al – Aluminum
Zn – Zinc
Fe – Iron
Sn – Tin
Pb – Lead
H – Hydrogen
Cu – Copper
Ag – Silver
Au – Gold
In the above reactivity series of metals Potassium is the most reactive, while Gold is the least reactive.
In Fig. 3 above, the single replacement or displacement reaction occurred successfully because K is more reactive than Na, which made it possible for K to replace or displace Na. But, In the second example, reaction is not possible, because Ca is less reactive than K. In addition, see below, the reactivity series of halogens.
Reactivity Series of Halogens;
Fluorine
Chlorine
Bromine
Iodine
Flourine is the most reactive in the halogen reactivity series above while, Iodine is the least reactive.
Double Replacement or Displacement Reactions
In double replacement or displacement reactions, two compounds will combine to form two new compounds. See example in Fig. 4 below;
The positive ions on each substances reacting, will replace each other in the opposite directions, and form new products. When the compounds combining are acids and bases, the reaction is also known as neutralization reaction, as seen in the second example in Fig. 4, above.
Combustion Reaction
In combustion reactions, substances react with oxygen to form oxides of the positive ions plus water. See example in Fig. 5 below;
Complete combustion proceeds with sufficient oxygen while incomplete combustion proceeds with insufficient oxygen.
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