Chemical Reactions And Equations

Balancing a chemical reaction is a very important step to satisfy the Law of Conservation of Mass. According to the law the total mass of the reactants should be equal to the total mass of the products formed.

Balancing a chemical reaction is just a trial and error method. While balancing, one has to ensure that the total number of molecules of an element at the reactant side should be equal to total number of molecules on product side.

Fe + H₂O → Fe₃O₄ + H₂

Now in the above reaction, iron on the product side has three molecules so let us multiply the iron on reactant side with 3.

3Fe + H₂O → Fe₃O₄ + H₂

There are four molecules of oxygen on product side. So let us multiply the water molecule on reactant side with 4.

3Fe + 4H₂O → Fe₃O₄ + H₂

Now there are eight molecules of hydrogen on reactant side. So let us make eight molecules on the product side also by multiplying hydrogen on product side with 4.

3Fe + 4H₂O → Fe₃O₄ + 4H₂

The reaction is as follows:

N₂ + 3H₂⇋ 2NH₃ + Heat

The liberation oh heat confirms the exothermic nature of the reaction.

Iron articles lose their shine gradually when exposed to the atmosphere. Iron is a reactive metal. Thus when exposed to atmosphere it reacts with atmospheric oxygen and moisture to form an iron oxide which is commonly called rust. Rust is a brownish coloured layer which gets developed over the surface of iron over a period of time. The reaction for the given change is as follow:

2Fe(s) + 3H₂O(aq) → Fe₂O₃(s) + 3H₂↑(g)

Reduction is widely used in metallurgical industries to reduce the metal oxide to metals. One of the best examples of reduction is reduction of iron oxide to iron in the blast furnace. The reaction is as follows:

3Fe₂O₃ + CO → CO₂ + 2Fe₃O₄

Fe₃O₄ + CO → CO₂ + 3FeO

FeO + CO → CO₂ + Fe

Copper Sulphate exists in two forms. One form is the hydrated copper sulphate whose chemical formula is CuSO₄.5H₂O and hydrated copper sulphate is blue colour in appearance.

When hydrated copper sulphate is heated, the water molecule gets evaporated to form anhydrated copper sulphate which is white in colour.

CuSO₄.5H₂O → CuSO₄ + 5H₂O

When we add water externally to anhydrate copper sulphate, it again turns blue in colour.

Silver bromide is a light-sensitive compound that is it gets decomposed when exposed to light.

So when silver bromide is exposed to sunlight, it gets decomposed to give silver metal and bromine gas is liberated. The reaction is called a photolysis reaction. The word photolysis can be broken into two parts photo means light and lysis means breaking. So photolysis means breaking of a compound in the presence of light.

Silver bromide is widely used in photography.

The reaction is given as follows:

2AgBr→ 2Ag + Br₂

Exothermic reaction is reaction in which heat is generated during the reaction and endothermic reaction is one in which heat is absorbed from the surrounding during the reaction.

A. Electrolysis of Water

During the electrolysis of water, heat is required to break the water molecule and hence the reaction is endothermic.

B. Burning of natural gas

During the burning of natural gas heat is generated and hence it is an exothermic reaction.

C. Decomposition of calcium carbonate

To break calcium carbonate heat is required and hence it is an endothermic reaction.

D. Burning of magnesium ribbon in air

Burning of magnesium ribbon is a highly exothermic reaction and so much heat is generated that the ribbon gives off UV rays during the reaction.

The silver is sensitive to light hence, silver compounds are stored in dark coloured bottles.

Similarly, silver chloride is a light-sensitive compound that is it gets decomposed when exposed to light.

So, when silver chloride is exposed to sunlight, it gets decomposed to give silver metal and chlorine gas is liberated. The reaction is an example of a photolysis reaction.

The word photolysis can be broken into two parts photo means light and lysis means breaking. So photolysis means breaking of a compound in the presence of light.

The reaction is given as follows:

2AgCl → 2Ag + Cl₂

When calcium oxide [quicklime] is added to water, it reacts vigorously with water to form calcium hydroxide [also known as slaked lime] with the liberation of large amount of heat.

Corrosion is a natural process of wasting of the metal due to the reaction of the metal with environmental factors like moisture, oxygen etc to form corresponding hydroxides, oxides on the surface of the metal.

Corrosion contributes to the major loss of metal in terms of its quality and usefulness with time. Corrosion generally degrades the base metal in terms of important properties like strength, appearance and permeability to liquids and gases. Corrosion in some cases can be useful as it protects the base metal from further reaction eg corrosion in case aluminium as it forms aluminium oxide and protects the base metal.

Rancidity is a condition which is related to unsaturated fats present in the food items. The aerial oxidation of the unsaturated fats present in the food items over long exposure to environment which leads to unpleasant odor and flavor is called as rancidity.

The fatty substances present in the food gets converted to hydroperoxides due to long exposure to air and this hydroperoxides gets decomposed to give aldehydes, ketones and hydrocarbons. Some of this decomposed organic compounds have unpleasant odor and flavor thereby degrading the quality of food item.

(i) The reaction is as follows:

When potassium chloride reacts with silver nitrate, a white precipitate of silver chloride is formed.

This reaction is a type of Precipitation reaction.

(ii) The reaction is as follows:

2FeSO₄→ Fe₂O₃ + SO₂ + SO₃

In the above reaction, ferrous sulphate decomposes to give reddish brown solids of iron oxide and the gas liberated is sulphur dioxide and sulphur trioxide which gives an odour of burning sulphur.

The reaction is as follows:

Pb (CH₃COO)₂ + HCl → PbCl₂ + CH₃COOH

In the above reaction there are two acetate molecules on reactant side and only one molecule on product side. So let us balance it first.

Pb (CH₃COO)₂ + HCl → PbCl₂ + 2CH₃COOH

Now there are two chlorine molecules on product side and only one chlorine molecule on reactant side. So the overall balanced reaction can be written as follows:

Pb (CH₃COO)₂ + 2HCl → PbCl₂ + 2CH₃COOH

This reaction belongs to double displacement type of reaction as it involves exchange of ions.

The reaction is as follows:

Na + C₂H₅OH → C₂H₅ONa + H₂

In the above reaction there are seven molecules of hydrogen on product side and six molecules on reactant side. So let us first balance the number of hydrogen.

Na + 2C₂H₅OH → 2C₂H₅ONa + H₂

Now there are 12 molecules of hydrogen on both the sides. Bu there are two molecules of sodium on product side and only one molecule on reactant side. So the overall balanced reaction can be written as follows:

2Na + 2C₂H₅OH → 2C₂H₅ONa + H₂

This reaction is a displacement reaction in which sodium displaces hydrogen from ethanol to form sodium ethoxide.

The reaction is as follows:

Fe₂O₃ + CO → Fe + CO₂

There are four molecules of oxygen on reactant side and only two molecules on product side. So let us first make the number of oxygen molecules same on both sides.

Fe₂O₃ + 3CO → Fe + 3CO₂

Now there are six molecules of oxygen on reactant and product side. Also the number of carbon molecules is same on both the sides. But there two molecules of iron on reactant side and only one molecule on product side. So the overall balanced equation can be written as follows:

Fe₂O₃ + 3CO → 2Fe + 3CO₂

This is a reduction reaction in which iron (III) oxide is getting reduced to iron metal.

The reaction is as follows:

H₂S + O₂→ S + H₂O

In the above equation there two oxygen molecules on reactant side and only one molecule on product side. So let us first balance the number of oxygen molecules on both sides first.

H₂S + O₂→ S + 2H₂O

Now there are four molecules of hydrogen on product side and only two molecules on reactant side. So let us now balance the number of hydrogen molecules on both sides.

2H₂S + O₂→ S + 2H₂O

Finally there are two sulphur molecules on reactant side and only one sulphur molecule on product side. So the overall balanced equation can be written as follows:

2H₂S + O₂→ 2S + 2H₂O

This reaction is also a type of displacement reaction in which oxygen replaces sulphur from hydrogen sulphide to form water.

Mg + Cl₂→ MgCl₂

In the above reaction,

At Reactant side there one molecule of magnesium and on the product side also there is only one molecule of magnesium.

Also at reactant side, there are two molecules of chlorine and at product side also there are two molecules of chlorine.

So the reaction is self-balanced.

It is a combination reaction as two reactants combine to form one single product.

This reaction has one molecule of oxygen on the reactant side and at the product side, there are two molecules of oxygen. So let us first make the oxygen molecules two on the reactant side.

2HgO → Hg + O₂

Now there are two molecules of mercury on the reactant side and only one molecule on the product side. So the total balanced reaction is as follows:

2HgO → 2Hg + O₂

It is thermal decomposition reaction as lead oxide decomposes on being heated to give lead metal.

In the above reaction, there are two molecules of sodium on the product side and only one molecule on the reactant side. So the balanced reaction is as follows:

2Na + S → Na₂S

It is a combination reaction as two reactants combine to form one single product.

In the reaction, there are four molecules of chlorine on the reactant side and only two molecules of chlorine on the product side. So let us first balance it.

TiCl₄ + Mg → Ti + 2MgCl₂

Now there are two molecules of magnesium on the product side and only one molecule on the reactant side. So the total balanced reaction is as follows:

TiCl₄ + 2Mg → Ti + 2MgCl₂

It is a displacement reaction in which the more reactive metal displaces the less reactive from its compound.

This is a self balanced chemical reaction as the number of molecules on reactant side is same as that of the number of molecules on product side.

It is combination reaction as two reactants combine to form one single product.

In the reaction oxygen molecules is not balanced on reactant and product side.

2H₂O₂→ H₂O + O₂

Now there are four molecules of hydrogen on reactant side and only two molecules at product side. So total balanced reaction is as follows:

2H₂O₂→ 2H₂O + O₂

It is photolysis reaction as hydrogen peroxide is decomposed in the presence of ultraviolet light to give water and oxygen.

(a) The salt of iron which is green in colour is Iron [II] Sulphate. It occurs in hydrated form and its chemical formula is FeSO₄.7H₂O [Ferrous Sulphate Heptahydrate]. It is also commonly called green vitriol.

(b) According to the above-mentioned description, the reaction is a thermal decomposition reaction as ferrous sulphate decomposes to iron [III] oxide and oxides of sulphur [sulphur dioxide and sulphur trioxide] on heating. So the black colour mass obtained at the end of the reaction is Iron [III] oxide and the odour of the burning of sulphur is due to oxides of sulphur formed in the reaction.

(c) The reaction is as follows:

2FeSO₄→ Fe₂O₃ + SO₂ + SO₃

(a) Element B is the most reactive element. Element B has replaced element A in the first reaction and also element B has replaced element C in the second reaction, so element B has to be the most reactive element.

(b) Element C is the least reactive element. Element C is replaced by both element A and B from its compound and hence it is the least reactive element.

(c) Reaction between oxide of A and element B is a reduction reaction as element A is reduced from its oxide state to its elemental state.

The reaction between sulphate of element C and B is displacement reaction in which a more reactive element [in this case B] replaces a less reactive element [in this case C] from its compound.

Reaction between oxide of C and element A is a reduction reaction as element C is reduced from its oxide state to its elemental state.

The word redox is a combination of two words reduction and oxidation. So a redox reaction is the type of reaction in which reduction as well as oxidation of elements takes place simultaneously.

For the First reaction,

Pb₃O₄ + 8HCl → 3PbCl₂ + Cl₂ + 4H₂O

In this reaction lead is losing its oxide state to form lead chloride. Hence lead undergoing reduction reaction.

On the other hand chlorine from hydrochloric acid is oxidized as it separated from hydrogen to give off chlorine gas.

For the second reaction,

CuO + H₂→ Cu + H₂O

In the above copper is getting reduced from its oxidized state to its free elemental state.

Hydrogen is getting oxidized from its free state to water molecule.

(a) A reaction in which is a single product is formed from two or more reactants is a combination reaction. The example of combination reaction is as follows:

H₂ + O₂→ H₂O

(b) Exothermic reaction is a reaction in which heat generated during the reaction process. So the reaction mixture becomes warm is a type of exothermic reaction. So an example of an exothermic reaction is as follows:

N₂ + 3H₂→ 2NH₃ + Heat

(c) Precipitation reaction is the reaction in which an insoluble mass is formed at the end of the reaction. The example of such reaction is as follows:

Double displacement reaction is a type of reaction which involves the exchange of ions.

Example of Double Displacement Reaction:

Mix ferrous sulphate solution with sodium hydroxide solution. The reaction gives a dirty green precipitate of ferrous hydroxide. The reaction is as follows:

Aluminium sheets do not corrode easily as aluminium when exposed to atmosphere, aluminium oxide is formed at the surface of the metal. Aluminium oxide is not porous and hence inhibit any further reaction of the metal with the surrounding.

Copper on the other hand react with the carbonic acid present in the atmosphere to form copper carbonate and hence it imparts greenish color to the copper vessels. During the rains carbonic acid get easily dissolved in the rain water and hence react with copper vessel to give a green coating on the metal.

(a) The colour of lead nitrate is white. When lead nitrate is heated it decomposes to give yellow coloured lead oxide and brown coloured nitrogen dioxide gas is liberated.

(b) The two gases evolved during the reaction are nitrogen dioxide and oxygen.

(c) The reaction is as follows:

(d) This reaction is thermal decomposition reaction as lead nitrate gets decomposed on the application of heat to give corresponding compounds.

(e) The example of this type of reaction is as follows:

2FeSO₄→ Fe₂O₃ + SO₂ + SO₃

The above-mentioned solutions can be kept safely in a copper container instead of an aluminium container.

Copper is a less reactive metal and is placed below hydrogen and aluminum in the activity series and hence copper would not react with the solutions.

On the other hand aluminum is more reactive metal and it will react with the solutions to form corresponding compounds.

The activity series of metals is as follows:

(i) Corrosion is a natural process of wasting of metal due to reaction of the metals with environmental factors like moisture, oxygen etc to form corresponding metallic compounds. The metal undergoing corrosion losses its strength, appearance and its efficiency.

Corrosion generally takes place under following conditions:

1. Exposure of metals to humid climatic conditions for a long period of time

2. Exposure of metals to reactive gases and liquids for long period of time.

3. Environmental condition of the place where metal is placed like temperature of the surrounding, moisture content in the air, etc.

(ii) The chemical formula for rust is Fe₂O₃.nH₂O(s).

Where n is the water of crystallization.

The rust is formed by the following equation:

The iron hydroxide formed dehydrates to produce Fe₂O₃.nH₂O(s).

Rancidity is the aerial oxidation of unsaturated fatty acids present in the food items. To prevent this oxidation following measures can be taken:

1. Keeping the food in air-tight containers

2. Packing the food at low temperatures

3. Addition of anti-oxidants to the food items.

4. Adding nitrogen gas during the packaging of food.

(a) The reaction is as follows:

Ca (OH)₂ + CO₂→ CaCO₃ + H₂O

This reaction is a self-balanced reaction as number of molecules on reactant side is same as that on the product side.

(b) The reaction is as follows:

PCl₅ + H₂O → H₃PO₄ + HCl

In this reaction there are five chlorine molecules on reactant side and only one molecule on the product side. So let us make the number of chlorine molecules 5 on product side also.

PCl₅ + H₂O → H₃PO₄ + 5HCl

Now there are eight molecules of hydrogen on product side and only two molecules on reactant side. So the total balanced reaction is as follows:

PCl₅ + 4H₂O → H₃PO₄ + HCl

(c) The reaction is as follows:

Zn + AgNO₃→ Zn (NO₃)₂ + Ag

In the above reaction there are two nitrate molecules on product side and only one nitrate molecule on reactant side. So let us first balance it.

Zn + 2AgNO₃→ Zn (NO₃)₂ + Ag

Now there two molecules of silver on reactant side and only one molecule on product side. So the total balanced equation is as follows:

Zn + 2AgNO₃→ Zn (NO₃)₂ + 2Ag

(d) The reaction is as follows:

Na + H₂O → NaOH + H₂

In the above reaction there three molecules of hydrogen on product side and only two molecules on reactant side. Let us first make the number molecules of hydrogen on product side even in number.

Na + H₂O → 2NaOH + H₂

Now there are two molecules of hydrogen on reactant side and four molecules on product side. So let us first balance it.

Na + 2H₂O → 2NaOH + H₂

Now there two molecules of sodium on product side and only one molecule on reactant side. So the total balanced equation is as follows:

2Na + 2H₂O → 2NaOH + H₂

(e) The reaction is as follows:

Al + CuCl₂→ AlCl₃ + Cu

In the above reaction there are two molecules of chlorine on reactant side and three molecules of chlorine on product side. Let us first make the number of chlorine molecules even on product side.

Al + CuCl₂→ 2AlCl₃ + Cu

Now there are six molecules of chlorine on product side. So let us make it six molecules of chlorine on reactant side also.

Al + 3CuCl₂→ 2AlCl₃ + Cu

After making the chlorine molecules same on both sides, the number of copper molecule son product side is only one and on reactant side it is three. So let us make the number of copper molecules equal on both sides.

Al + 3CuCl₂→ 2AlCl₃ + 3Cu

Finally there two molecules of aluminium on product side and only one molecule on reactant side. So the total balanced equation can be written as follows:

2Al + 3CuCl₂→ 2AlCl₃ + 3Cu