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Types of Chemical Reactions

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When chemical substances react, the reaction typically does not go to completion. The term "chemical reaction" conjures up images of a mad scientist laboratory. Chemical reactions describe the conversion of chemical substances which are called reactants, aducts or substrates in case of catalyzed reactions. 

To identify chemical reactions by the temperature oscillation, a similar but somewhat different viewpoint is needed. For simple chemical reactions, in which a single elementary process is involved, the rate of a chemical reaction depends on the temperature and the state of conversion.

What is a Chemical Reaction?

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When certain element and compounds are combined with other elements and compounds entirely new substances can be produced. This interaction is called chemical reaction. The starting substances are called reactants and the created substances are called products. A substance that helps a chemical reaction occur faster without undergoing any change itself is called a catalyst. Chemical reactions are normally permanent.

There are different types of chemical reaction.
  • An exothermic reaction gives out heat.
  • An endothermic reaction causes a drop in temperature or requires a heat source to occur.
  • Thermal decomposition uses heat to cause compounds to break down.
  • Electrolysis is a reaction in which compounds are broken down with the use of electricity.
  • Neutralization is when an acid and base react to make a salt or neutral solution.
  • Oxidation is when a substance gains oxygen.
  • Reduction is when a substance loses oxygen.
  • Displacement is when a more reactive element displaces or pushes out a less reactive element from its compound.

Writing a Chemical Reaction

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In a chemical reaction, the atoms stay the same. But they join up in different combinations to form new molecules. Chemical reactions can be described by writing down the atoms and molecules before the reaction and the atoms and molecules after the reaction. The number of atoms before will be the same as the number of atoms after. Chemists write the reaction as an equation. This shows what happens in the chemical reaction. 

For example, the reaction that takes place when xenon reacts with fluoride can be written like 

Xe + F2 $\rightarrow$ XeF2 

Chemical Reaction

Solving Chemical Equations

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Equations are symbolic representations of the chemical changes that occur in a chemical reaction at the atomic/molecular level. The symbols that chemist use to depict chemical reactions are designed to specify what the atoms are doing when a reaction occurs. Studying chemistry is much easier once you learn to visualize what reaction equations are indicating symbolically. 

Chemical Reaction Example

Solved example based on chemical equations are given below.


Problem

2 atoms of hydrogen combine with one atom of oxygen to give one molecule of water. How many grams of hydrogen are needed to react completely with 6.4g of oxygen gas?

Solution

The chemical reaction is 
2H + O $\rightarrow$ H2O
2H  $\rightarrow$  H2
2 atom
2 mole
  1 atom
1 mole 
  1 molecule
1 mole 
2 $\times$ 1.0g 1 $\times$ 16.0g molar mass of H atom = 1.0 g/mol
molar mass of O atom = 16.0 g/mol
2g
 16g  
? 6.4g  

So mass of hydrogen required = $\frac{2g}{16g}$ $\times$ 6.4g = 0.8g

Solved Example

Question: How many moles of Fe3O4 can be made from 0.599 moles of Fe according to the following?
 3Fe + 2O2 $\rightarrow$ Fe3O4
Solution:
There is one mole Fe3O4 involved for every three moles of Fe. If Fe cancel and the answer in moles is Fe3O4.

$0.599\ moles\ Fe \times \frac{1\ mole\ Fe_{3}O_{4}}{3\ moles\ Fe}$ = 0.186 moles Fe3O4


5 Types of Chemical Reaction

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Chemical reaction is a process at the molecular or ionic level by which one or more types of substances are transformed into one or more new types of substances by different modes of combination. There are five different types of chemical reactions. 

1. Combination reaction
A reaction involving the formation of compound from two or more substances is called a combination reaction.
For example, formation of sodium chloride.

$2Na(s) + Cl_2(g) \rightarrow 2NaCl(s)$

2. Combustion reaction
The combustion is a process of burning and most combustion involves reaction with oxygen. For example, the combustion of liquid ethanol called ethyl alcohol is given below.

$C_2H5OH(l) + O_2(g) \rightarrow CO_2(g) + H_2O(g)$

3. Decomposition reaction
A decomposition reaction is a process in which one compound decomposes or splits to form two or simpler compounds or elements.

For example, decomposition of calcium carbonate is given below.
$CaCO_3(s) \rightarrow CaO(s) + CO_2(g)$

4. Single replacement reaction
An element reacts with a compound and results in the displacement of an element or group from the compound. 

For example,
$Zn(s) + CuCl_2(aq) \rightarrow ZnCl_2(aq) + Cu(s)$

In this reaction, Zn substitutes for Cu.

5. Double replacement reaction
This reaction is also called metathesis reaction, which involves the exchange of two groups or two ions among the reactants. This reaction often results in an insoluble product from soluble reactants and the insoluble compound formed is called a precipitate.

For example,
$AgNO3(aq) + NaCl(aq) \rightarrow AgCl(s) + NaNO_3(aq)$

This reaction involves the formation of a precipitate of AgCl.