Chemical Reactions And Equations

Balanced chemical equation: A chemical equation in which the number of atoms of reactants and number of atoms of products is called a balanced equation.

Every chemical equation should be balanced because:

⇒According to the law of conservation of mass, atoms are neither created not destroyed in chemical reactions.

⇒It means the total mass of the products formed in chemical reaction must be equal to the mass of reactants consumed.

NaOH + H₂SO₄ Na₂SO₄H₂O

Balanced equation: 2NaOH + H₂SO₄Na₂SO₄ + 2H₂O

Explanation:

⇒Step 1: Write the given unbalanced equation

NaOH + H₂SO₄Na₂SO₄ + H₂O

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. Thus, let us consider sodium atom. If we multiply 2 in the reactant (in NaOH), we will get the equal number of atoms as in product (Na₂SO₄)

⇒Step 4: Write the resulting equation:

2NaOH + H₂SO₄Na₂SO₄ + H₂O

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is not balanced yet. As the number of oxygen, hydrogen and Sulphur atoms are unequal on the two sides. First balance the hydrogen number.

⇒Step 6: Now, let us consider hydrogen atom. If we multiply 2 in the product (in H₂O), we will get the equal number of atoms as in reactants (in 2NaOH and H₂SO₄)

⇒Step 7: Write the resulting equation:

2NaOH + H₂SO₄Na₂SO₄ + 2H₂O

⇒Step 8: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is balanced now.

⇒Step 9: Write down the final balanced equation:

2NaOH + H₂SO₄Na₂SO₄ + 2H₂O

Hg(NO₃)₂ + KI HgI₂ + KNO₃

Balanced equation: Hg(NO₃)₂ + 2KI HgI₂ + 2KNO₃

Explanation:

⇒Step 1: Write the given unbalanced equation

Hg(NO₃)₂ + KI HgI₂ + KNO₃

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. First, let us consider iodine atom. If we multiply 2 in the reactant (in KI), we will get the equal number of atoms as in product (HgI₂)

⇒Step 4: Write the resulting equation:

Hg(NO₃)₂ + 2KI HgI₂ + KNO₃

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is not balanced yet. As the number of oxygen, nitrogen and potassium atoms are unequal on the two sides.

First balance the potassium number.

⇒Step 6: Now, let us consider potassium atom. If we multiply 2 in the product (KNO₃), we will get the equal number of atoms as in reactant (in KI)

⇒Step 7: Write the resulting equation:

Hg(NO₃)₂ + 2KI HgI₂ + 2KNO₃

⇒Step 8: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is balanced now.

⇒Step 9: Write down the final balanced equation:

Hg(NO₃)₂ + 2KI HgI₂ + 2KNO₃

H₂ + O₂ H₂O

Balanced equation: 2H₂ + O₂ 2H₂O

Explanation:

⇒Step 1: Write the given unbalanced equation

H₂ + O₂ H₂O

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. First, let us consider oxygen atom. If we multiply 2 in the product (in H₂O), we will get the equal number of atoms as in reactant (O₂)

⇒Step 4: Write the resulting equation:

H₂ + O₂ 2H₂O

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is not balanced yet. As the number of hydrogen atoms are unequal on the two sides.

⇒Step 6: Now, let us consider hydrogen atom. If we multiply 2 in the reactant (H₂), we will get the equal number of atoms as in product (in 2H₂O)

⇒Step 7: Write the resulting equation:

2H₂ + O₂ 2H₂O

⇒Step 8: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is balanced now.

⇒Step 9: Write down the final balanced equation:

2H₂ + O₂ 2H₂O

KClO₃KCl + O₂

Balanced equation: 2KClO₃2KCl + 3O₂

Explanation:

⇒Step 1: Write the given unbalanced equation

KClO₃KCl + O₂

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. Thus, let us consider oxygen atom. If we multiply 2 in the product (in KClO₃) and 3 in the reactant (in O₂) we will get the equal number of atoms in both sides.

⇒Step 4: Write the resulting equation:

2KClO₃KCl + 3O₂

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is not balanced yet. As the number of potassium and chlorine atoms are unequal on the two sides. First balance the potassium atom.

⇒Step 6: If we multiply 2 in the product (in KCl), we will get the equal number of atoms as in reactant (in 2KClO₃)

⇒Step 7: Write the resulting equation:

2KClO₃2KCl + 3O₂

⇒Step 8: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is balanced now.

⇒Step 9: Write down the final balanced equation:

2KClO₃2KCl + 3O₂

C₃H₈ + O₂ CO₂ + H₂O

Balanced equation: C₃H₈ + 5O₂ 3CO₂ + 4H₂O

Explanation:

⇒Step 1: Write the given unbalanced equation

C₃H₈ + O₂ CO₂ + H₂O

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. Thus, first let us consider hydrogen atom. If we multiply 4 in the product (in H₂O), we will get the equal number of atoms as in reactant (in C₃H₈)

⇒Step 4: Write the resulting equation:

C₃H₈ + O₂ CO₂ + 4H₂O

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is not balanced yet. As the number of carbon and oxygen atoms are unequal on the two sides.

First balance the carbon atom.

⇒Step 6: If we multiply 3 in the product (in CO₂), we will get the equal number of atoms as in reactant (in C₃H₈)

⇒Step 7: Write the resulting equation:

C₃H₈ + O₂ 3CO₂ + 4H₂O

⇒Step 8: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is not balanced yet. As the number of oxygen atoms are unequal on the two sides.

⇒Step 9: Now, we consider oxygen atoms. If we multiply 5 in the reactant (in O₂), we will get the equal number of atoms as in products (in 3CO₂ and 4H₂O)

⇒Step 10: Write the resulting equation:

C₃H₈ + 5O₂ 3CO₂ + 4H₂O

We find that the equation is balanced now.

⇒Step 11: Write down the final balanced equation:

C₃H₈ + 5O₂ 3CO₂ + 4H₂O

Zn + AgNO₃→ Zn(NO₃)₂ + Ag

Balanced equation: Zn + 2AgNO₃→ Zn(NO₃)₂ + 2Ag

Explanation:

⇒Step 1: Write the given unbalanced equation

Zn + AgNO₃→ Zn(NO₃)₂ + Ag

Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. Thus, let us consider nitrogen atom first. If we multiply 2 in the reactant (in AgNO₃), we will get the equal number of atoms as in product (Zn(NO₃)₂)

⇒Step 4: Write the resulting equation:

Zn + 2AgNO₃→ Zn(NO₃)₂ + Ag

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is not balanced yet. As the number of silver atoms are unequal on the two sides.

⇒Step 6: Now, let us consider silver atom. If we multiply 2 in the product (in Ag), we will get the equal number of atoms as in reactant (in 2AgNO₃)

⇒Step 7: Write the resulting equation:

Zn + 2AgNO₃→ Zn(NO₃)₂ + 2Ag

⇒Step 8: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is balanced now.

⇒Step 9: Write down the final balanced equation:

Zn + 2AgNO₃→ Zn(NO₃)₂ + 2Ag

Al + CuCl₂ → AlCl₃ + Cu

Balanced equation: 2Al + 3CuCl₂ → 2AlCl₃ + 3Cu

Explanation:

⇒Step 1: Write the given unbalanced equation

Al + CuCl₂ → AlCl₃ + Cu

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. Thus, let us consider chlorine atom first. If we multiply 2 in the product (in AlCl₃) and 3 in the reactant (in CuCl₂) we will get the equal number of atoms in both sides.

⇒Step 4: Write the resulting equation:

Al + 3CuCl₂ → 2AlCl₃ + Cu

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is not balanced yet. As the number of aluminum and copper atoms are unequal on the two sides.

First balance the aluminum atom.

⇒Step 6: If we multiply 2 in the reactant (in Al), we will get the equal number of atoms as in product (in 2AlCl₃)

⇒Step 7: Write the resulting equation:

2Al + 3CuCl₂ → 2AlCl₃ + Cu

⇒Step 8: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is not balanced yet. As the number of copper atoms are unequal on the two sides.

⇒Step 9: If we multiply 3 in the product (in Cu), we will get the equal number of atoms as in product (in 3CuCl₂)

⇒Step 10: Write the resulting equation:

2Al + 3CuCl₂ → 2AlCl₃ + 3Cu

⇒Step 11: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is now balanced.

⇒Step 12: Write down the final balanced equation:

2Al + 3CuCl₂ → 2AlCl₃ + 3Cu

H₂ + Cl₂→ HCl

Balanced equation: H₂ + Cl₂→ 2HCl

Explanation:

⇒Step 1: Write the given unbalanced equation

H₂ + Cl₂→ HCl

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. First, let us consider hydrogen atom. If we multiply 2 in the product (in HCl), we will get the equal number of atoms as in reactant (H₂)

⇒Step 4: Write the resulting equation:

H₂ + O₂ 2HCl

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is now balanced yet.

⇒Step 6: Write down the final balanced equation:

2H₂ + Cl₂ 2HCl

NH₄NO₃ → N₂O + H₂O

Balanced equation: NH₄NO₃ → N₂O + 2H₂O

Explanation:

⇒Step 1: Write the given unbalanced equation

NH₄NO₃ → N₂O + H₂O

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. Thus, let us consider hydrogen atom first. If we multiply 2 in the product (in H₂O), we will get the equal number of atoms as in the reactant (in NH₄NO₃)

⇒Step 4: Write the resulting equation:

NH₄NO₃ → N₂O + 2H₂O

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is now balanced yet.

⇒Step 6: Write down the final balanced equation:

NH₄NO₃ → N₂O + 2H₂O

Ca(OH)₂ + HNO₃→ H₂O + Ca(NO₃)₂

Balanced equation: Ca(OH)₂ + 2HNO₃→ 2H₂O + Ca(NO₃)₂

Type of reaction: Double displacement reaction

Mg + I₂→ MgI₂

Balanced equation: Mg + I₂→ MgI₂

Type of reaction: Decomposition reaction

Mg + HCl → MgCl₂ + H₂

Balanced equation: Mg + 2HCl → MgCl₂ + H₂

Type of reaction: Displacement reaction

Zn + CaCl₂→ ZnCl₂ + Ca

Balanced equation: Zn + CaCl₂→ ZnCl₂ + Ca

Type of reaction: Displacement reaction

On heating calcium carbonate, it decomposes to calcium oxide and carbon dioxide. The reaction is:

CaCO₃→ CaO + CO₂

The above reaction is an example of thermal decomposition reaction in which decomposition take places in the presence of heat.

Note: Decomposition reaction is a reaction in which only one reactant decomposes into two or more products.

Precipitation reaction – When two reactants exchange their constituents chemically and form products in which one of them product is insoluble in water, the reaction takes place is called precipitation reaction.

For example: when aqueous lead nitrate and potassium iodide are mixed together, they form lead iodide which is insoluble in water. Lead iodide is called precipitate. The reaction is:

Pb(NO₃)₂ + KI → PbI₂ + 2KNO₃

precipitate

Difference between displacement and double displacement reaction:

Note:

Displacement reaction –

Decomposition reaction –

The decomposition reaction which occurs in the presence of sunlight is called photochemical reaction.

For example: 2AgBr → 2Ag + Br₂

⇒In the above reaction, silver bromide (AgBr) decomposes to silver and bromine in sunlight.

⇒Light colour of AgBr changes to gray due to sunlight.

Exothermic reaction: A reaction in which heat is released when reactants changes into products.

Respiration is considered as an exothermic reaction because:

⇒In respiration, a large amount of heat energy is released when oxidation of glucose takes place.

Difference between displacement and double displacement reaction:

Note: Double displacement reaction –

In the given reaction, MnO₂ + 4HCl MnCl₂ + 2H₂O + Cl₂

HCl is oxidized to Cl₂ and MnO₂ is reduced to MnCl₂

Explanation: As we know that oxidation is reaction that involves the removal of hydrogen and reduction is a reaction that involves the removal of oxygen.

Thus, HCl is oxidized and MnO₂ is reduced.

Oxidation – reduction reaction: When oxidation and reduction takes place at the same time, then the reaction is called oxidation-reduction reaction.

Oxidation: losing of electrons Reduction: gaining of electrons

For example:

CuO + H₂→ Cu + H₂O

⇒In the reaction, CuO loses oxygen atom which means that reduction of CuO (copper oxide) takes place.

⇒H₂ (hydrogen) takes up oxygen atom.

⇒As a result, formation of water takes place. This means hydrogen undergoes oxidation.

Another example:

The reaction involved is:

2AgNO₃ + Cu → Cu(NO₃)₂ + 2Ag

In the above reaction, when copper is mixed with silver nitrate, copper displaces the silver from silver nitrate and form its own ions as Cu(NO₃)₂

Corrosion – When some metals are exposed to moisture, air, acids etc. they tarnish due to the formation of metals oxide on their surface. This process is called corrosion.

Corrosion can be prevented by:

⇒Shielding the surface, the metal surface from oxygen and moisture.

⇒By painting, oiling, greasing, galvanizing, chrome plating or making alloys.

⇒Galvanizing is a method of protecting iron from rusting by coating them a thin layer of zinc.

When we use old, left over cooking oil for making foodstuff, it is found to have foul odour called rancidity.

⇒Rancidity is an oxidation reaction.

⇒If food is cooked in such oil, its taste also changes.

⇒When oils or fats are left aside for a long time, they undergo air oxidation and become rancid.

⇒Rancidity in the food stuff cooked in oil or ghee is prevented by using antioxidants.

Balanced equation: C₆H₁₂O_6(s) 2C₂H₅OH_(s) +2CO_2(g)

Explanation:

⇒Step 1: Write the given unbalanced equation

C₆H₁₂O₆ C₂H₅OH+CO₂

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. Thus, first let us consider hydrogen atom. If we multiply 2 in the product (in C₂H₅OH), we will get the equal number of atoms as in reactant (in C₆H₁₂O₆)

⇒Step 4: Write the resulting equation:

C₆H₁₂O₆ 2C₂H₅OH+CO₂

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is not balanced yet. As the number of carbon and oxygen atoms are unequal on the two sides.

First balance the carbon atom.

⇒Step 6: If we multiply 2 in the product (in CO₂), we will get the equal number of atoms as in reactant (in C₆H₁₂O₆)

⇒Step 7: Write the resulting equation:

C₆H₁₂O₆ 2C₂H₅OH+2CO₂

⇒Step 8: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is balanced now.

⇒Step 9: Write down the final balanced equation:

C₆H₁₂O₆ 2C₂H₅OH+2CO₂

Fe + O₂ Fe₂O₂

Balanced equation: 2Fe_(s) + O_2(g) Fe₂O_2(s)

Explanation:

⇒Step 1: Write the given unbalanced equation

Fe + O₂ Fe₂O₂

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. Thus, let us consider Fe atom. If we multiply 2 in the reactant (in Fe), we will get the equal number of atoms as in product (in Fe₂O₂)

⇒Step 4: Write the resulting equation:

2Fe + O₂ Fe₂O₂

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is balanced now.

⇒Step 6: Write down the final balanced equation:

2Fe + O₂ Fe₂O₂

NH₃ +Cl₂ N₂ +NH₄Cl

Balanced equation: 8NH_3(g) + 3Cl_2(g) N_2(g) + 6NH₄Cl_(s)

Explanation:

⇒Step 1: Write the given unbalanced equation

NH₃ +Cl₂ N₂ +NH₄Cl

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. Thus, first let us consider hydrogen atom. If we multiply 4 in the reactant (in NH₃) and 3 in product (in NH₄Cl), we will get the equal number of atoms as in both the sides.

⇒Step 4: Write the resulting equation:

4NH₃ +Cl₂ N₂ + 3NH₄Cl

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is not balanced yet. As the number of chlorine and nitrogen atoms are unequal on the two sides.

First balance the chlorine atom.

⇒Step 6: If we multiply 3 in the reactant (in Cl₂) and 2 in the product (in 3NH₄Cl), we will get the equal number of atoms as in both the sides.

⇒Step 7: Write the resulting equation:

4NH₃ + 3Cl₂ N₂ + 6NH₄Cl

_⇒Step 8: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is not balanced yet. As the number of nitrogen atoms are unequal on the two sides.

Balance the nitrogen atom.

⇒Step 9: If we multiply 2 in the reactant (in 4NH₃) we will get the equal number of atoms as in products (in N₂ and 6NH₄Cl)

⇒Step 10: Write the resulting equation:

4NH₃ + 3Cl₂ N₂ + 6NH₄Cl

_⇒Step 11: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is balanced now.

⇒Step 12: Write down the final balanced equation:

4NH₃ + 3Cl₂ N₂ + 6NH₄Cl

Na+ H₂O NaOH + H₂

Balanced equation: 2Na_(s) + 2H₂O_(aq)2NaOH_(aq) + H_2(g)↑

Explanation:

⇒Step 1: Write the given unbalanced equation.

Na+ H₂O NaOH + H₂

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. Thus, first let us consider hydrogen atom. If we multiply 2 in the reactant (in H₂O) and 2 in product (in NaOH), we will get the equal number of atoms as in both the sides.

⇒Step 4: Write the resulting equation:

Na+ 2H₂O 2NaOH + H₂

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is not balanced yet. As the number of sodium atoms are unequal on the two sides.

Balance the sodium atom.

⇒Step 6: If we multiply 2 in the reactant (in Na), we will get the equal number of atoms as in product (in 2NaOH).

⇒Step 7: Write the resulting equation:

2Na+ 2H₂O 2NaOH + H₂

_⇒Step 8: Now check whether the equation is balanced or not by comparing the atoms.

We find that the equation is balanced now.

⇒Step 9: Write down the final balanced equation:

2Na+ 2H₂O 2NaOH + H₂

BaCl₂ + Na₂SO₄→ BaSO₄ + NaCl

Balanced equation:

Explanation: BaCl_2(aq) + Na₂SO_4(aq)→ BaSO_4(s)↓+ 2NaCl_(aq)

⇒Step 1: Write the given unbalanced equation

BaCl₂ + Na₂SO₄→ BaSO₄ + NaCl

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having unequal no. of atoms on both sides. First, let us consider sodium atom. If we multiply 2 in the product (in NaCl), we will get the equal number of atoms as in product (Na₂SO₄)

⇒Step 4: Write the resulting equation:

BaCl₂ + Na₂SO₄→ BaSO₄ + 2NaCl

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is balanced now.

⇒Step 6: Write down the final balanced equation:

BaCl₂ + Na₂SO₄→ BaSO₄ + 2NaCl

NaOH + HCl → NaCl + H₂O

Balanced equation: NaOH_(aq) + HCl_(aq)→ NaCl_(aq) + H₂O_(l)

Explanation:

⇒Step 1: Write the given unbalanced equation

NaOH + HCl → NaCl + H₂O

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

We find that the equation is already balanced.

⇒Step 3: Write down the balanced equation:

NaOH + HCl → NaCl + H₂O

Zn + HCl → ZnCl₂ + H₂

Balanced equation: Zn_(s) + 2HCl_(aq)→ ZnCl_2(aq) + H_2(g)↑

Explanation:

⇒Step 1: Write the given unbalanced equation

Zn + HCl → ZnCl₂ + H₂

⇒Step 2: Compare the number of atoms of reactants with the number of atoms of products.

⇒Step 3: Now, first we consider the element having uSnequal no. of atoms on both sides. Thus, first let us consider hydrogen atom. If we multiply 2 in the reactant (in HCl), we will get the equal number of atoms as in product (in H₂)

⇒Step 4: Write the resulting equation:

Zn + 2HCl → ZnCl₂ + H₂

⇒Step 5: Now check whether the equation is balanced or not by comparing the atoms

We find that the equation is balanced now.

⇒Step 6: Write down the final balanced equation:

Zn + 2HCl → ZnCl₂ + H₂

⇒It is given that ‘X’ is a shiny brown colored element. This means ‘X’ is a copper metal.

⇒When copper (X) is heated in air, it becomes black in color due to the deposit of copper oxide on its surface.

⇒The reaction takes place:

2Cu + O₂→ 2CuO

Brown Black

We apply paint on iron articles to prevent the corrosion and rusting of iron. It decreases the rate of the process of rusting of iron.

The use of keeping food in air tight containers is to prevent oxidation and to slow down the oxidation process, otherwise the food undergoes oxidation and becomes rancid.