Chemical Reaction And Catalyst

Because Fe is changing its oxidation state of +3 in FeCl₃ to + 2 in FeCl_2..Hence, it is a reduction reaction

The reaction in which a single substance is splitted into simple molecules is called dissociation reaction.

Electron releasing substances are known as reducing agents because these elecrons which are released later on reduces other species.

Reversible reactions are those which occur in both forward and backward direction.

Substances which increases the rate of a reaction are called catalysts. These substances effects the rate of a reaction and itself remains unaffected at the end.

Enzymes are the biological catalysts present in the human body.

As in the above reaction magnesium is gaining oxygen. Hence, it is oxidized.

As reversible reactions are those which occur in both forward and backward direction. Hence, for reversible reaction ⇋ sign is used.

In autocatalytic reactions the product formed catalyses the reaction.

Exothermic reactions proceed with the evolution of heat energy.

The changes in which the chemical composition and the chemical properties of the substance changes are known as chemical change.

Finely divided powdery form of Raney Ni is the catalyst which converts vegetable ghee.

Vegetable oil + H₂ Vegetable ghee

The types of catalysis are: -

i. Based on their physical state:

a. Heterogeneous catalyst

b. Homogeneous catalyst

ii. Based on their action:

a. Positive catalyst

b. Negative catalyst

c. Auto-catalyst

d. Bio-catalyst

This is a replacement reaction as in this reaction the more reactive element Zinc is replacing the less reactive element Copper from its salt or compound.

The reactions in which both oxidation and reduction takes place simultaneously are known as redox reactions.

An example of a redox reaction is:-

Fe₂O₃ + 3CO → 2Fe + 3CO₂

In the above reaction ferric oxide (Fe₂O₃) is reduced into iron (Fe) by losing the oxygen atoms attached to it and carbon monoxide (CO) is oxidized into carbon dioxide (CO₂) by gaining the oxygen atoms.

Reaction which occurs in both the directions i.e the products are formed from the reactants and the reactants are being formed from the product at the same time are known as reversible reactions. In these reactions, the concentration of the reactants never becomes zero.

Example: Formation of ammonia is a reversible change as shown:

N₂ + 3H₂⇌ 2NH₃

Catalytic promoter – Those substances which are added with catalysts in a chemical reaction to increase the efficiency or activity of the catalyst is known as the catalytic promoter.
Example:

N₂ + 3H₂ 2NH₃
In Haber’s process for the synthesis of ammonia, traces of molybdenum increases the activity of finely divided iron which acts as a catalyst hence, acts like a catalytic promoter.
Catalytic poison - Those substances which are added with catalysts in a chemical reaction to decrease the efficiency or activity of the catalyst are known as a catalytic poison.

Example:

N₂ + 3H₂ 2NH₃

In the above reaction of synthesis of ammonia carbon monoxide decreases the efficiency of the iron catalyst and hence, acts like a catalytic poison.

The reaction between a strong acid and a strong base which forms salt and water is known as a neutralization reaction.

A typical neutralization looks like:

Example is given below:

There are two types of reaction based on speed: -

i. Fast reactions

ii. Slow reactions
Example:
Rusting is a slow reaction

Burning and explosions are very fast reactions

An example of a thermal decomposition reaction is the decomposition of calcium carbonate to produce calcium oxide and carbon dioxide on heating at 473K.This could be seen in the following reaction:-

CaCO₃ → CaO + CO₂

Catalysts are the substances which changes the rate of the chemical reaction but itself remains unchanged after the completion of the reaction.

Example: NO acts as a catalyst in the conversion of sulphur dioxide to sulphur trioxide as shown:

2SO₂ + O₂ 2SO₃

The basic principle of balancing a chemical reaction is that on both the sides of the arrow there must be equal number of atoms of each type according to the basic rule of chemical combination i.e mass conservation law. While balancing the empirical formula of the compound must not be changed.

The reactions in which both oxidation and reduction takes place simultaneously are known as redox reactions.

Example: Reaction of ferric oxide with carbon monoxide to form iron and carbon dioxide as shown below:-

In the above reaction ferric oxide (Fe₂O₃) is reduced into iron (Fe) by losing the oxygen atoms attached to it and carbon monoxide (CO) is oxidized into carbon dioxide (CO₂) by gaining the oxygen atoms.

Combustion of coal is an addition reaction. It is represented by the following equation:-

C(s) + O₂(g) → CO₂(g)

Here oxygen is added to carbon (of hydrocarbon) to produce carbon dioxide gas in the product.

The pH of the solution obtained by reacting a strong acid with a strong base is 7 and the resulting mixture would be neutral in nature.

Addition reaction – Reactions in which two or more substances or reactants combine to form a new single product are termed as addition reaction.

Example- C(s) + O₂(g) → CO₂(g)

Dissociation reaction – Reactions in which a single reactant decomposes to form two or more product are termed as dissociation reaction.

Example - 2H₂O(l) → 2H₂(g) + O₂(g)

The above reaction is a double displacement reaction.

Double displacement reaction – The reactions in which a mutual exchange of ions takes place between two reactants are termed as double displacement reaction.

Here potassium is displaced by silver from its salt to form silver chloride and the displaced potassium then reacts with nitrate ion to form potassium nitrate. Hence, it is a double displacement reaction.

Oxidation reaction – On the basis of the exchange theory of electrons an oxidation reaction could be termed as that in which an atom, element, molecule or an ion loses an electron.

Example – Na → Na⁺ + e ^-

Reduction reaction – On the basis of the exchange theory of electrons a reduction reaction could be termed as that in which an atom, element, molecule or an ion gains an electron.

Example – Cl + e ^- → Cl ^–

The type of catalysts are as follows –

iii. Based on their physical state:

a. Heterogeneous catalyst :

When in a reaction the catalysts, reactants, and products are in different physical states then the catalyst is known as heterogeneous catalyst.

Example-

Vegetable oil (l) + H₂ (g) Vegetable ghee (l)

b. Homogeneous catalyst:

When in a reaction the catalysts, reactants and products are in the same phase then the catalyst is known as homogeneous catalyst.

Example:-

2SO₂ (g) + O₂ (g) 2SO₃ (g)

iv. Based on their action:

a. Positive catalyst:

The catalysts which increases the rate of a reaction are termed as positive catalyst.

Example:

2KClO₃ 2KCl + 3O₂

b. Negative catalyst:

The catalysts which decreases the rate of a reaction are termed as negative catalyst.

Example:

2H₂O₂ 2H₂O + O₂

c. Auto-catalyst;

When the product formed in a reaction itself behaves as a catalyst, then it is known as auto-catalyst.

Example:

CH₃COOC₂H₅ + H₂O → CH₃COOH + C₂H₅0H

d. Bio-catalyst:

The catalyst which increases the rate of the biochemical reactions occurring in a living organism are termed as bio-catalyst. These are also known as enzymes.

Example:

Maltose Glucose

The types of dissociation reaction are:-

i. Electrolysis:

In this method electrical energy is used to decompose the reactant into products. To bring about the decomposition electrical energy or electric current is passed through the fused salt of the substance.

Example – Electrolysis of water gives hydrogen and oxygen as shown –

2H₂O 2H₂ + O₂

ii. Thermal decomposition:

In this method heat energy is used to decompose the reactant into products.

Example – Decomposition of calcium carbonate as shown to give calcium oxide and oxygen s is a thermal decomposition reaction –

CaCO₃ CaO + O₂

iii. Photolysis:

In this method energy from the sun is used to decompose the reactant into products.

Example – Decomposition of hydrogen bromide as shown –

2HBr → H₂ + Br₂

Chloroform directly reacts with oxygen from the air and gets oxidized to form a very poisonous gas known as phosgene. Hence, in order to decrease the rate of this reaction some amount of ethyl alcohol is added in chloroform to store it so that the rate of creation of phosgene is reduced and it is safe for use.

In the reaction between a strong base and a weak acid, the acid does not get completely ionized and some amount of acid is present in unionized form. So, when we take equal moles of a weak acid and strong base and mix them together them also some OH^- remains excess in the solution and the solution becomes basic in nature.

(i) Cu + ZnSO₄→ CuSO₄ + Zn

The above replacement reaction is not possible because Copper is less reactive then Zinc. Hence, it would not able to replace Zinc from its compound (ZnSO₄₎.

(ii) Fe + CuSO₄→ FeSO₄→ FeSO₄ + Cu

The above replacement reaction is possible because Copper is less reactive then Iron. Hence, Iron would easily replace copper from its compound (CuSO₄ ) to form ferrous sulphate( FeSO₄).

(i) C + O₂→ CO₂

The above reaction is an oxidation reaction in which the carbon atom is gaining the oxygen and is oxidized.

(ii) Mg + CI₂→ MgCI₂

The above reaction is an oxidation reaction because here a more electronegative atom which is chlorine is being added to magnesium.

(iii) ZnO + C → Zn + CO

The above reaction is a redox reaction in which zinc is getting reduced as it is losing oxygen atoms and carbon is getting oxidized as it is gaining the oxygen atoms.

(iv) Fe₂O₃ + 3CO → 2Fe + 3CO₂

The above reaction is a redox reaction in which ferric oxide (Fe₂O₃) is reduced into iron (Fe) and carbon monoxide (CO) is oxidized into carbon dioxide (CO₂) by gaining the oxygen atoms.

The various types of chemical reactions are:

i. Addition reactions:

The reaction in which two or more reactants combine to form a single product are known as addition reaction. In this new type of bonds are formed between the reactants.

Ex- C(s) + O₂(g) → CO₂(g)

ii. Replacement reactions:

In these reactions a more reactive element replaces a less reactive element from its compound.

Ex- Fe + CuSO₄→ FeSO₄→ FeSO₄ + Cu

Double displacement reaction:

This is a subcategory of replacement reactions in which mutual exchange of ions occurs between two reactants.

Ex – CuSO₄ + 2NaOH → Cu(OH)₂ + Na₂SO₄

iii. Dissociation reactions:

These are the reactions in which a single reactant decompose to form two or more products. There are various types of dissociation reaction as follows: -

The types of dissociation reaction are :-

a) Electrolysis:

In this method electrical energy is used to decompose the reactant into products. Electric energy is passes through the fused salt of the substance.

Example – Electrolysis of water gives hydrogen and oxygen as shown –

2H₂O 2H₂ + O₂

b) Thermal decomposition:

In this method heat energy is used to decompose the reactant into products.

Example – Decomposition of calcium carbonate as shown to give calcium oxide and oxygen–

CaCO₃ CaO + O₂

c) Photolysis:

In this method energy from the sun is used to decompose the reactant into products.

Example – Decomposition of hydrogen bromide s shown –

2HBr → H₂ + Br₂

iv. Reversible reactions:

The reactions those which occur in both forward and backward direction are known as reversible reactions.

Ex- N₂ + 3H₂⇌ 2NH₃

v. Irreversible reactions:

Those reactions which flow in only one direction and products are formed from the reactants are known as irreversible reactions.

Ex- C + O₂→ CO₂

Oxidation:

The reactions in which oxygen or a more electronegative elements are added to any substance.

Or

The reactions in which oxygen or a more electronegative elements are added to any substance.

Or

Process in which a chemical species losses electrons.

Reduction:

The reactions in which oxygen or more electronegative elements are removed from any substance.

Or

The reactions in which hydrogen or a more electropositive elements are added to any substance.

Or

Process in which a chemical species gains electrons.

The reactions in which both oxidation and reduction takes place simultaneously are known as oxidation reduction reactions.

Ex- Fe₂O₃ + 3CO → 2Fe + 3CO₂

In the above reaction ferric oxide (Fe₂O₃) is reduced into iron (Fe) by losing the oxygen atoms attached to it and carbon monoxide (CO) is oxidized into carbon dioxide (CO₂) by gaining the oxygen atoms. Hence, it is an oxidation reduction reaction.

Properties of catalyst:

i. Catalysts only change the rate of a chemical reaction but itself remain unchanged in composition and amount.

ii. Catalysts are sufficient in small amounts only.

iii. For a specific reaction there is a specific catalyst and a single catalyst cannot catalyse all the reaction.

iv. Catalysts does not initiate a chemical reaction but only increases the rate of the reaction,

v. In reversible reactions catalysts equally increases the rate of forward and backward reaction.

vi. Catalysts are more efficient and effective at a particular temperature. By changing the temperature we can control their activity.

The types of catalysts are as follows –

i. Based on their physical state:

a. Heterogeneous catalyst :

When in a reaction the catalysts, reactants and products are in different physical states then the catalyst is known as heterogeneous catalyst.

Example-

Vegetable oil (l) + H₂ (g) Vegetable ghee (l)

b. Homogeneous catalyst:

When in a reaction the catalysts, reactants and products are in the same phase then the catalyst is known as homogeneous catalyst.

Example:-

2SO₂ (g)+ O₂(g) 2SO₃(g)

ii. Based on their action:

a. Positive catalyst:

The catalysts which increases the rate of a reaction are termed as positive catalyst.

Example:

2KClO₃ 2KCl + 3O₂

b. Negative catalyst:

The catalysts which decreases the rate of a reaction are termed as a negative catalyst.

Example:

2H₂O₂ 2H₂O + O₂

c. Auto-catalyst;

When the product formed in a reaction itself behaves as a catalyst, then it is known as auto-catalyst.

Example:

CH₃COOC₂H₅ + H₂O → CH₃COOH + C₂H₅0H

d. Bio-catalyst:

The catalyst which increases the rate of the biochemical reactions occurring in a living organism is termed as bio-catalyst. These are also known as enzymes.

Example:

Maltose Glucose

Steps of writing a chemical equation are: -

i. At first, reactants are written followed by a single arrow and then products are written.

ii. If reactants or products are more than one in number then they are separated by a + sign.

iii. The Mass conservation law is followed while writing a chemical reaction. According to which in both the sides of the arrow there must be an equal number of atoms of each type.

iv. Mass of reactants and mass of products must be equal.

v. While balancing a chemical equation first of all atoms other than oxygen and hydrogen are balanced.

vi. After balancing the chemical; equation the physical state of each substance is represented by writing - s, l, g in brackets after each substance indicating solid, liquid and gaseous state respectively.

vii. Substances in solution are represented by writing aq in the bracket after each substance.

viii. Reaction conditions for a reaction to occur like temperature, pressure, catalyst etc. are written above the arrow.

ix. In case of an exothermic and endothermic reaction, amount of energy is written with (+) and (-) sign respectively along with products in R.H.S of the equation.

x. Delta (∆) symbol is sometimes used to represent chemical changes in a reaction.