Chemical Reactions And Their Types

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

Every chemical equation should be balanced because:

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

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

Hence, the correct option is (d)

In the reaction (b) SiO₂ + 2Mg →Si + 2MgO

Check whether the equation is balanced or not by comparing the atoms:

We found that the equation is completely balanced. Hence, the option (b) is correct.

Chemical displacement is a reaction in which more reactive element displaces the less reactive element from their compounds and form a new compound itself.

For example:

Zn + 2HCl → ZnCl₂ + H₂

In the reaction, zinc (being more reactive) has displaced hydrogen from HCl and form a new compound, i.e., ZnCl₂.

In a chemical reaction, new substances are formed. Hence, dissolving sugar in water is not an example of a chemical reaction because no new substances are formed during the change.

2SO₂ + O₂→ 2SO₃↑

In the given reaction, sulphur dioxide and oxygen (reactants) combined together to form a single product, i.e., SO₃. Hence, this reaction is an example of decomposition reaction.

Balanced equation: Cu + 2H₂SO₄→ CuSO₄ + SO₂↑ + 2H₂O

Step 1: Write the unbalanced equation

Cu + H₂SO₄→ CuSO₄ + SO₂↑ + 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 the oxygen atom. If we multiply 2 in the reactant (in H₂SO₄) and 2 in the product (in H₂O), we will get the equal number of oxygen atoms in both sides.

Step 4: Write the resulting equation:

Cu + 2H₂SO₄→ CuSO₄ + SO₂↑ + 2H₂O

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:

Cu + 2H₂SO₄→ CuSO₄ + SO₂↑ + 2H₂O

Balanced equation: 3Fe + 4H₂O → Fe₃O₄ + 4H₂

Step 1: Write the unbalanced equation

Fe + H₂O → Fe₃O₄ + 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 Fe atom. If we multiply 3 in the reactant (in Fe), we will get the equal number of atoms as in product (in Fe₃O₄)

Step 4: Write the resulting equation:

3Fe + H₂O → Fe₃O₄ + 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 oxygen atoms is unequal on the two sides. Hence, balance the oxygen atom.

Step 6: If we multiply 4 in the reactant (in H₂O), we will get the equal number of oxygen atoms on both sides.

Step 7: Write the resulting equation:

3Fe + 4H₂O → Fe₃O₄ + H₂

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 hydrogen atoms is unequal on the two sides.

Step 9: Now, we consider hydrogen atoms. If we multiply 2 in the product (in H₂), we will get the equal number of hydrogen atoms as in reactants.

Step 10: Write the resulting equation:

3Fe + 4H₂O → Fe₃O₄ + 2H₂

We find that the equation is balanced now.

Step 11: Write down the final balanced equation:

3Fe + 4H₂O → Fe₃O₄ + 2H₂

Balanced equation: CH₄ + 2O₂→ CO₂ + 2H₂O

Step 1: Write the unbalanced equation

CH₄ + 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 the hydrogen atom. If we multiply 2 in the product (in H₂O), we will get the equal number of hydrogen atoms as in reactant (in CH₄)

Step 4: Write the resulting equation:

CH₄ + O₂→ CO₂ + 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 oxygen atoms is unequal. Hence, balance the oxygen atom.

Step 6: If we multiply 2 in the reactant (in O₂), we will get the equal number of oxygen atoms on both sides.

Step 7: Write the resulting equation:

CH₄ + 2O₂→ CO₂ + 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:

CH₄ + 2O₂→ CO₂ + 2H₂O

Differences between a physical change and chemical change:

Physical change: It is a temporary change in which no new substance is formed and the mass of the substance remains the same. Hence, dissolving the salt in H₂O and melting of an ice cube are physical changes.

Chemical change: It is a permanent change in which a new substance is formed and the weight of the substance changes. Hence, rusting of iron and burning of fuel are chemical changes.

i) Chemical combination: It is the reaction in which two or more reactants combine together to form a new product.

For example:

ii) Chemical decomposition: It is a reaction in which a single reactant breaks up into two or more products. For this purpose, sufficient energy is provided.

For example:

iii) Chemical displacement: It is the reaction in which a more reactive element displaces the less reactive from their compounds.

For example:

CuSO₄ + Fe → FeSO₄ + Cu

In the above reaction, Fe being more reactive displaces the Cu from its compound (CuSO₄) and form a new compound (FeSO₄)

iv) Double displacement reaction: In this reaction, the two reactants exchange their constituents chemically and form two products.

For example:

BaCl₂ + ZnSO₄ → BaSO₄ + ZnCl₂

In this reaction, exchange of ions of Ba and Zn are taking place.

a) CaCO₃ + heat → CaO + CO₂↑

In the given reaction, CaCO₃ used sufficient energy in the form of heat and breaks up into calcium oxide (CaO) and carbon dioxide gas. Hence, this reaction is an example of decomposition reaction.

b) 2AgNO₃ + Cu → Cu(NO₃)₂ + 2Ag ↓

In the given reaction, copper being more reactive displaces silver (Ag) from its compound (AgNO₃) and form a new compound (Cu(NO₃)₂. Hence, this reaction is an example of displace reaction.

c) 2SO₂ + O₂→ 2SO₃↑

In the given reaction, sulphur dioxide and oxygen (reactants) combined together to form a single product, i.e., SO₃. Hence, this reaction is an example of combination reaction.

d) NaCl + AgNO₃→ AgCl ↓ +NaNO₃

In the given reaction, the exchange of ions of Na and Ag are taking place. Hence, this reaction is an example of double displacement reaction.

The advantages of writing a chemical equation using formulae and symbols:

For example: C + O₂→ CO₂

The equationusing symbols

i) This method helps us in knowing the reactants and products only.

ii) This method also helps us in knowing the correct relation between the quantities of reactants consumed and products formed C:O₂: CO₂ = 1:1:1

The type of chemical reaction associated with this observation is an exothermic reaction.

i) It is a reaction in which heat is also released along with the formation of products.

ii) Plastic papers releases too much energy.

iii) The energy they release is very harmful to the environment.

The possible products obtained by the combustion of butane are carbon dioxide and water and energy are also released.

The chemical reaction for this process is:

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

i) Rancidity is an oxidation reaction.

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

iii) By keeping food in air tight container helps to slow down oxidation.

iv) Rancidity in the food stuff cooked in oil or ghee is also prevented by using antioxidants.

v) Usually antioxidants such as nitrogen gas flushed into bags containing food.

CuSO₄ + Fe → FeSO₄ + Cu

i) Iron is more reactive than copper.

ii) In the above reaction, iron being more reactive than copper displaces it from its compound (CuSO₄)

iii) As a result, a new compound FeSO₄ is formed.

iv) The above reaction is an example of a single displacement reaction.

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

Respiration is considered as an exothermic reaction because:

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

ii.The glucose combines with the oxygen in the cells of our body and gives energy.

In chemical equations, oxygen is represented as O₂ but not O and chlorine is represented as Cl₂ but not Cl because oxygen and chlorine are diatomic molecules (consisting of only two atoms). They both exist in nature as diatomic molecules.

Use of plastic must be avoided or minimized because
i) Plastic is a non- biodegradable substance.

ii) Non- biodegradables substances are the substances which do not get easily decomposed.

iii) Burning of plastic causes air, water, and soil pollution.

iv) They produce harmful and toxic gases.

v) They cause health problems too. Their toxic chemicals can damage several body organs.