Chemical Reactions And Equations

a. To prevent rusting, a layer of zinc metal is applied on iron sheets.

Explanation:

Galvanization is a method to prevent rusting.

i. In this method, a thin layer of zinc is applied on iron sheets to prevent rusting/corrosion.

ii. First rusting of zinc takes place (more electropositive than iron).

iii. After few seasons, zinc layer goes away.

iv. Then, iron starts rusting.

b. The conversion of ferrous sulphate to ferric sulphate is oxidation reaction.

Explanation:

Oxidation means losing of electrons.

2FeSO₄→ Fe₂(SO₄)₃

Ionic reaction Fe²⁺ + SO₄^2-→ 2Fe³⁺ + 3SO₄^2-

As we can observe that in ionic reaction that Fe²⁺ changes to Fe³⁺. In this, the positive charge increases by one unit. This means ferrous ion loses one electron. Thus, the above reaction is an oxidation reaction.

c. When electric current is passed through acidulated water electrolysis of water takes place.

Explanation:

On passing electric current through acidulated water (a water contains acid), water decomposes into hydrogen and oxygen gases. This decomposition takes place due to the presence of electrical energy. The reaction takes place is called electrolysis.

Electrolysis: 2H₂O(l) → 2H₂↑ + O₂↑

d. Addition of an aqueous solution of ZnSO₄ to an aqueous solution of BaCl₂ is an example of double displacement reaction.

Explanation:

On addition of ZnSO₄ and BaCl₂, the following reaction takes place:

ZnSO₄ + BaCl₂→ ZnCl₂ + BaSO₄

In the reaction, the exchange of ions are taking place. The reaction in which exchange of ions take place to form precipitate are called double displacement reaction.

When oxidation and reduction takes place simultaneously, the reaction is called redox reaction.

Oxidation: losing of electrons Reduction: gaining of electrons

Redox Reaction = Reduction + oxidation

For example:

CuO + H₂→ Cu + H₂O

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

ii. H₂ (hydrogen) takes up oxygen atom.

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

iv. Oxidation and reduction are taking place at the same time, thus it a redox reaction.

Another example:

Decomposition of hydrogen peroxide is a slow process:

2H₂O₂(l) → 2H₂O + O₂↑ (slow reaction)

But we can increase the rate of reaction by using a particular catalyst, i.e., Manganese dioxide powder (MnO₂).

A catalyst is a substance which increases the rate of reaction without causing any chemical change.

Reactants – The substances which take part in a chemical reaction are called reactants.

Products – The substances which are formed due to the formation of new bonds in a chemical reaction are called products.

For example:

Here, H₂ and O₂ take part in the chemical reaction, hence they are reactants. H₂O is formed by the formation of new bonds; hence it is a product.

Types of reaction with reference to oxygen and hydrogen:

i. Decomposition reaction

2H₂O₂→ 2H₂O + O₂

In this reaction hydrogen peroxide undergoes decomposition

to form water and oxygen gas.

ii. Redox reaction

CuO + H₂→ Cu + H₂O

In this reaction, oxidation and reduction taking place at the

same time.

iii. Electrolysis of water (decomposition)

2H₂O(l) → 2H₂↑ + O₂↑

In this decomposition of water takes place to release hydrogen and oxygen gas.

Reaction between NaOH and water: NaOH + H₂O → Na⁺ + OH^-

Reaction between CaO and water : CaO + H₂O → Ca(OH)₂ + heat

Endothermic reaction: In endothermic reaction, heat is either absorbed from the surroundings or heat has to supplied from outside. It means an endothermic reaction needs or takes in heat to continue.

For example: When a solid ammonium chloride (NH₄Cl) is dissolved into water, you will observe that the tube becomes colder.

NH₄Cl (s) + H₂O → NH₄Cl (aq) – Heat

In the above reaction, heat is absorbed from surroundings.

Combination reaction: When two or more reactants combine in a reaction to form a single product, it is called a combination reaction.

For example: A magnesium strip is heated in the presence of air to form a new product, i.e., magnesium oxide (MgO)

Mg + O₂→ MgO

In the above reaction, the combination of Mg and O₂ leads to the formation of manganese oxide.

Balanced equation: When the number of atoms of elements in the reactants is equal to the number of atoms of those elements in the products, such a equation is called ‘balanced equation’.

For example: H₂ + O₂→ 2H₂O

In the above table, you can see that number of atoms of reactants are equal to the number of atoms of products. Thus, the reaction is a ‘balanced equation’.

Displacement reaction: The reaction in which the ion of a more reactive element displaces the ion of a less reactive metal by forming its own ions. Such reaction is called displacement reaction.

In short, displacement reaction is a reaction in which a more reactive element displaces the less reactive element to form its new compound.

For example: CuSO₄ + Zn → ZnSO₄ + Cu

In the reaction, Zn²⁺ ions formed from Zn atoms take the place of Cu²⁺ ions in copper sulphate (zinc is more reactive).

It means that Zn displaces Cu from CuSO₄.

When limewater (CaOH)₂ is passed through a gas, CO₂, the following reaction takes place:

⇒ In this reaction, when limewater comes in contact with the gas released in the form of an effervescence, it turns milky. This is chemical test for carbon dioxide gas.

⇒ When limewater turns milky, it is confirmed that the effervescence is of carbon dioxide.

⇒ ‘Lime water turning milky’ is the test of carbon dioxide gas.

On addition of dilute HCl in pieces of Shahabad tile, the rate of reaction is very slow. On the other hand, on addition of dilute HCl in powder form of Shahabad tile, the rate of reaction is fast because:

⇒ The rate of reaction depends upon the size of the particles of the reactants.

⇒ Smaller the size of reactant, higher will be its rate of reaction.

⇒ Greater the size of reactant, lesser will be its rate of reaction.

When concentrated sulphuric acid is diluted with water, a very large amount of heat is released. It is very dangerous and can cause accident.

⇒ To avoid this, a required amount of water is taken in a beaker.

⇒ Small quantity of sulphuric acid is added into the water.

⇒ Constant stirring has to be done to decrease the releasing heat.

⇒ As a result, only a small amount of heat is released.

Note: In chemical labs, it always advised that we should add acid in water, not water in acid.

It is recommended to use air tight container for storing oil for long time because:

⇒ When oil comes in contact with air, it undergoes air oxidation.

⇒ This can make the oil rancid (a foul smell).

⇒ Thus, it is advised to use air tight container for storing oil to prevent it from exposure of air.

⇒ The picture given shows the corrosion od iron.

⇒ The chemical formula of rust is Fe₂O₃.H₂O.

⇒ The rust on iron does not form by a simple reaction of oxygen with iron surface. The rust is formed by an electrochemical reaction.

⇒ Different regions on the surface of iron become anode and cathode.

⇒ Fe is oxidised to Fe²⁺ (anode)

Fe (s) → Fe²⁺ (aq) + 2e^-

⇒ O₂ is reduced to form water (cathode)

O₂ (g) + 4H⁺ (aq) + 4 e- → 2H2O

⇒ When Fe²⁺ ions migrate from the anode region they react with water and further get oxidised to form Fe³⁺ ions.

⇒ A redish coloured hydrated oxide is formed from Fe³⁺ ions.

⇒ It is called rust which collects on the surface.

⇒ Due to various components of atmosphere, oxidation of metals takes place, consequently resulting in their damage. This is called ‘corrosion’.

⇒ Iron rusts and a redish coloured layer is collected on it.

⇒ This is corrosion of iron.

a. Fe + S → FeS

In the given reaction, Fe is giving 2 electrons to Sulphur. Sulphur is accepting those electrons. This means:

⇒ Fe undergoes oxidation (to lose electrons)

⇒ Sulphur undergoes reduction (to accept electrons)

b. 2Ag₂O → 4 Ag + O₂

⇒ Ag in Ag₂O has oxidation state= +1

Ag in Ag(s) has oxidation state = 0

This means Ag undergoes reduction

⇒ O in Ag₂O has oxidation state = -2

O in O₂ has oxidation state = 0

This means oxygen undergoes oxidation

c. 2Mg + O₂→ 2MgO

First write the half reactions:

Mg⁰ → Mg²⁺ + 2e^-

O₂ + 4e^-→ O^2-

⇒ Oxygen goes from 0 to -2. Thus, it undergoes reduction.

⇒ Magnesium goes from 0 to +2. Thus, it undergoes oxidation

d. NiO + H₂→ Ni + H₂O

First write the half reactions:

2H⁰ - 2e^-→ 2H¹

Ni²⁺ + 2e^-→ Ni⁰

⇒ Hydrogen goes from 0 to 1. Thus, it undergoes oxidation.

⇒ Nickel goes from 2 to 0. Thus, it undergoes reduction.

Balanced equation: H₂S₂O₇ + H₂O → 2H₂SO₄

Explanation:

⇒ Step 1: Write the given unbalance equation

H₂S₂O₇ + H₂O(l) H₂SO₄(l)

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

⇒ Step 3: Now, if we multiply 2 in the products, we will get the equal number of atoms as reactants.

⇒ Write down the final balanced equation:

H₂S₂O₇ + H₂O → 2H₂SO₄

Balanced equation: SO₂(g) + 2H₂S(aq) 3S(s) + 2H₂O (l)

Explanation:

⇒ Step 1: Write the given unbalanced equation

SO₂(g) + H₂S(aq) S(s) + H₂O (l)

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

⇒ Step 3: Now, let us consider oxygen atom. If we multiply 2 in the product (in H₂O), we will get the equal number of atoms as in reactants (SO₂)

⇒ Step 4: Write the resulting equation:

SO₂ + H₂S S + 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

sulphur and hydrogen 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 reactant (in H₂S), we will get the equal number of atoms as in product (H₂O)

⇒ Step 7: Write the resulting equation:

SO₂ + 2H₂S S + 2H₂O

⇒ 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

sulphur atom is unequal on the two sides.

⇒ Step 9: Now, let us consider sulphur atom. If we multiply 3 in the product (S), we will get the equal number of atoms as in reactants (SO₂ and H₂S)

⇒ Step 10: Write the resulting equation:

SO₂ + 2H₂S 3S + 2H₂O

⇒ Step 11: Now, compare the atoms of both the sides of all the elements. Write down the final balanced equation:

SO₂ + 2H₂S 3S + 2H₂O

Balanced equation: 2Ag + 2HCl 2AgCl + H₂

Explanation:

⇒ Step 1: Write the given unbalanced equation

Ag + HCl AgCl + 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, 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 (H₂)

⇒ Step 4: Write the resulting equation:

Ag + 2HCl → AgCl + 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

chlorine atom is unequal on the two sides.

First balance the chlorine number.

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

⇒ Step 7: Write the resulting equation:

Ag + 2HCl 2AgCl + 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

silver atom is unequal on the two sides.

⇒ Step 9: Now, let us consider silver atom. If we multiply 2 in the reactant (Ag), we will get the equal number of atoms as in product (AgCl)

⇒ Step 10: Write the resulting equation:

2Ag + 2HCl 2AgCl + H₂

⇒ Step 11: Now, compare the atoms of both the sides of all the elements. Write down the final balanced equation:

2Ag + 2HCl 2AgCl + H₂

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 2NaOH), 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 reactant (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 now balanced yet.

⇒ Step 11: Write down the final balanced equation:

2NaOH + H₂SO₄Na₂SO₄ + 2H₂O

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

Endothermic reaction: A reaction in which heat is either supplied or absorbed from the surroundings.

a. HCl + NaOH → NaCl + H₂O + heat

The given reaction is exothermic because in the reaction heat is released when reactants transformed into products.

b. 2KClO₃ (s) 2KCl(s) + 3O₂↑

The given reaction is an endothermic reaction because in the reaction, heat has been supplied to continue the process.

c. CaO + H₂O → Ca(OH)₂ + heat

The given reaction is an exothermic reaction because in the reaction heat is released when reactants transformed into products.

d. CaCO₃ (s) CaO(s) + CO₂↑

The given reaction is an endothermic reaction because in the reaction, heat has been supplied to continue the process.

Explanation:

⇒ BaCl₂ + ZnSO₄ → BaSO₄ + ZnCl₂

The given reaction is an example of double displacement reaction. In this reaction, exchange of ions of Ba and Zn are taking place.

Note: Double displacement reaction is a reaction in which the ions of metals exchange to form different products.

⇒ 2AgCl → 2Ag + Cl₂

The given reaction is an example of decomposition reaction. In the given reaction, AgCl decomposes into Ag and Cl_2.

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

⇒ CuSO₄ + Fe → FeSO₄ + Cu

The given reaction is an example of displacement reaction. In this reaction, the most reactive metal (Fe) displaces the other metal.

Note: Displacement reaction is a reaction in which the ions of the most reactive metals displaces the ions of the less reactive metal to form its own ions.

⇒ H₂O + CO₂→ H₂CO₃

The given reaction is an example of combination reaction. In this reaction, H₂O and CO₂ combines together to form H₂CO₃ (carbonic acid).

Note: Combination reaction is a reaction in which two reactants combine together to form a new product.