CHEMICAL REACTIONSfor Class DAE 1st Year Chemical Technology

MUHAMMAD SHAKAIB QURESHI

M.PHIL CHEMISTRY

CONTENT

• INTRODUCTION

• COLLISION THEORY OF MOLECULE

• TYPES OF CHEMICAL REACTIONS

Introduction

• Chemical reaction, a process in which one or more substances, the reactants, are converted to one or more different substances, the products. Substances are either chemical Element or Compound.

• Reactants are in left Hand Side Which Reacts together and formed products which are in right hand Side.

Combustion Reaction

How Chemical Reaction Happens ?Collision Theory of Molecules

Postulates• In order for a chemical reaction to take place, the reactants

must collide. The collision between the molecules in a chemicalreaction provides the kinetic energy needed to break thenecessary bonds so that new bonds can be formed.

• Sometimes, even if there is a collision, not enough kineticenergy is available to be transferred — the molecules aren’tmoving fast enough. You can help the situation somewhat byheating the mixture of reactants. The temperature is ameasure of the average kinetic energy of the molecules;raising the temperature increases the kinetic energy availableto break bonds during collisions.

Continue

• Sometimes, even if there is a collision, not enoughkinetic energy is available to be transferred — themolecules aren’t moving fast enough. You can helpthe situation somewhat by heating the mixture ofreactants. The temperature is a measure of theaverage kinetic energy of the molecules; raising thetemperature increases the kinetic energy available tobreak bonds during collisions.

• The molecules must also collide in the right orientation, or hit at the rightspot, in order for the reaction to occur.

• Here’s an example: Suppose you have an equation showing molecule A-Breacting with C to form C-A and B, like this:

• A-B + C→C-A + B• The way this equation is written, the reaction requires that reactant C

collide with A-B on the A end of the molecule. If it hits the B end, nothingwill happen. The A end of this hypothetical molecule is called the reactivesite, the place on the molecule that the collision must take place in orderfor the reaction to occur.

• If C collides at the A end of the molecule, then there’s a chance thatenough energy can be transferred to break the A-B bond. After the A-Bbond is broken, the C-A bond can be formed. The equation for this reactionprocess can be shown in this way:

• C~A~B→C-A + B• So in order for this reaction to occur, there must be a collision between C

and A-B at the reactive site. The collision between C and A-B has to transferenough energy to break the A-B bond, allowing the C-A bond to form.

Energy is required to break a bond between atoms.

ACTIVATION ENERGY

Factors Affecting on Chemical Reaction

• Nature of Reactant

• Catalyst

• Concentration

• Temperature

• Pressure

Example

Catalyzed Reaction

Types of Chemical Reactions

• Addition/Synthesis Reactions:

• Addition reactions, also known as synthesis reactions or direct combination reactions, involve two or more reactants combining to form a single, more complex product. Examples are the reaction of iron and sulfur to form iron sulfide, or, in organic chemistry, the reaction of ethene and bromine to form dibromoethane.

• Example: C2H4 + Br2 → C2H4Br2

• Decomposition Reactions:

• A decomposition reaction involves the breaking down of a chemical compound into elements or simpler compounds. It is sometimes defined as the opposite of a synthesis reaction. They can occur spontaneously, or be initiated by heat, a catalyst, or electrolysis. An example is the decomposition of hydrogen peroxide into hydrogen and oxygen.

• Example: 2H2O2 → 2H2O + O2

• Combustion Reactions:

• Combustion reactions involve oxygen reacting with another element or compound to produce energy in the form of heat & light. They are always exothermic. Complete combustion requires a plentiful supply of oxygen – in a limited supply, incomplete combustion occurs, and different products can be formed. When organic chemicals combust completely, the products always include carbon dioxide and water.

• Example: CH4 + 2O2 → 2H2O + CO2

• Neutralization Reactions:

• A neutralization reaction is one in which an acid and a base react to form a salt. Water is commonly produced as well. Often these reactions are exothermic, but endothermic neutralizations are possible. Neutralization reactions do not necessarily result in a pH of 7 – resultant pH is dependent on the strength of the acid and the base.

• Example: NaOH + HCl → NaCl + H2O

• Precipitation Reactions:

• A precipitation reaction is one in which aqueous compounds react to form an insoluble solid, called a precipitate. This solid can be suspended throughout the solution, or fall to the bottom of the reaction vessel. Whether or not the product of a reaction will form a precipitate is determined by solubility rules for ionic compounds.

• Example: 2NaOH(aq) +MgCl2(aq) → 2NaCl(aq) + Mg(OH)2(s)

• METATHESIS OR DOUBLE DISPLACEMENT REACTION

• In a double displacement or metathesis reaction two compounds exchange bonds or ions in order to form Different Compounds.

AB + CD → AD + CB

An example of a double displacement reaction occurs between sodium chlorideand silver nitrate to form sodium nitrate and silver chloride.

NaCl(aq) + AgNO3(aq) → NaNO3(aq) + AgCl(s)

• SUMMARY

THE END