Lesson 3: Chemical Reaction

Behavioural objectives: at the end of the lesson, you should be able to:

·         Define chemical reaction

·         Identify different types of chemical reaction through equation

·         Define rate of chemical reaction

·         State and explain the factors that affect rate of chemical reaction

·         Define chemical equilibrium

·         Derive equilibrium constant for chemical reactions

·         State le chatelier’s principle

·         State and explain the factors that affect equilibrium system

What is chemical reaction?

This is the process whereby two or more chemical substance react together to produce new substances.

A + B  →       C + D

Reactant          product

The substance that react together are called reactants while the new substance(s) formed is called product.

The product is usually different to the reactants in terms of physical and chemical properties. For example, water (H₂O) is made from the combination of hydrogen and oxygen molecules in ratio 2:1

2H_2(g) + O_2(g) → 2H₂O_(l)

Both hydrogen and oxygen are gases but when they combined to form water, the water formed is liquid at room temperature which has a distinct properties from its parent reactancts.

What are the types of chemical reactions?

1.      Combination reaction

2.      Decomposition reaction

3.      Displacement reaction

4.      Thermal decomposition reaction

5.      Thermal dissociation reaction

6.      Reversible reaction

7.      Endothermic reaction

8.      Exothermic reaction

9.      Double decomposition reaction

10.  Redox reaction

11.  Catalytic reaction

1.      Combination reaction: this is a type of reaction that involve  the addition of two or more simple elements or compounds forming a single compound or complex compound.

e.g. Na + Cl → NaCl (simple compound)

PbO₂ + SO₂  → PbSO₄ (complex compound)

2.      Decomposition reaction: this is a situation whereby a compound split into two or more compounds. E.g. Pb(NO₃)₂  →PbO₂ + 2NO₂

3.      Displacement reaction: this is a type of reaction on which one atom or element replace another atom or element from its compound. E.g. 2HBr + Cl₂ → 2HCl + Br₂

The ability of an atom or elements to displace another is determined by its position in the electrochemical series. In the above reaction, chlorine is more electronegative than bromine.

1.      Thermal decomposition reaction: this is a decomposition reaction that involved heat.

2.      Thermal dissociation reaction: this is kind of reversible reaction that involve heat. E.g. NH₄Cl_(s) ↔ NH3_(g) + HCl_{(g) .} in this reaction when heat is applied to ammonium chloride it will decompose to ammonia and hydrogen chloride gas, and when the two gases reach a cool region, they will recombine and form ammonium chloride. Meaning that the reaction is reversible. Note: that thermal dissociation is different from thermal decomposition in the sense that thermal decomposition is not reversible while thermal dissociation is reversible.

3.      Reversible reaction: this is a type of reaction in which the product can also recombine to give back the product. On the other hand, it’s a reaction that proceeds at both end it is usually represented by double arrow, one facing the right and the other facing the left. E.g. NH₄Cl_(s) ↔ NH3_(g) + HCl _(g)   

4.      Endothermic reaction: from the word “endo” it means internal while “thermic” means heat. Endothermic reaction is a type of reaction that needs heat from the surroundings to proceed. That is heat is absorbed from the environment. e.g.  A + B → C + D; ∆H ꞊ + where ∆H is the change in heat content of the reaction.

5.      Exothermic reaction: this is the opposite case of endothermic reaction that is heat is given off to the surroundings and change in its heat content is negative. E.g. A + B → C + D; ∆H ꞊ -

6.      Double decomposition reaction: this is a situation whereby two compounds decompose simultaneously to form another compounds by exchange of  radicals. E.g.                    NaCl + AgNO₃ → AgCl + NaNO₃

7.      Catalytic reaction: Any reactions that involve the use of catalyst is regarded as catalytic reaction. A catalyst is any chemical substance that speedup the rate of chemical reaction but does not takes place in the reaction. E.g 2KClO₃   MnO₂        3O₂   + 2KCl. In this reaction manganese (iv) oxide is used as the catalyst to speed up the decomposition of potassium Oxo chlorate (v). Hence the reaction is a catalytic reaction. While the act of using catalyst is known as catalysis

8.      Redox reaction: here we are having two things together i.e. oxidation and reduction reaction. Oxidation is the loss of electron while reduction is the gaining of electron. Therefore a redox reaction is the one in which both oxidation and reduction takes place simultaneously. Note that oxidation and reduction can also be defined in terms of oxygen and hydrogen.

Oxidation in terms of oxygen is the addition of oxygen while reduction is the removal of oxygen.

Oxidation in terms of hydrogen is the removal of hydrogen while reduction is the addition of hydrogen.  Therefore on this note, all chemical reaction can be seen as redox reaction in as much that they will involve any of the three definitions.   

chemical equilibrium and the rest objectives will be posted tomorrow by gods grace and the remaining part of IUPAC naming will be released soon please bear with us.