Chemical Reaction And Equation

When a chemical reaction occurs:

i. New substances are formed by breaking and making of new

bonds.

ii. Some gases may evolve during the reaction.

iii. Change in smell.

iv. Change in colour.

v. Change in state (liquid, solid or gaseous)

vi. Change in temperature.

When hydrogen reacts with oxygen in the presence of an electric current, formation of water takes place which conducts electricity.

At the cathode, the electrons and the hydrogen ions combine with oxygen to make water.

The reaction takes place is given as:

2H₂ + O₂→ 2H₂O

The reaction in which there is an exchange of ions between the reactant takes place is called double displacement reaction.

For example:

Na₂SO₄ + BaCl₂→ BaSO₄ + 2NaCl

Sodium Barium Barium Sodium sulphate chloride sulphate chloride

In the above reaction, the exchange of ions (SO₄^2- and Ba²⁺) takes place. The white precipitate of BaSO₄ is formed by the reaction of SO₄^2- and Ba²⁺. The other product formed NaCl remains in the solution.

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

We need to balance a skeletal chemical equation because:

i. According to the law of conservation of mass, mass (or atoms) are neither created nor destroyed in chemical reactions.

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

Chemical equations can be made more informative by the

following characteristics:

Physical state

There are three different states which are solid, liquid and gaseous. If the substance exists in solid state, it is represented by (s).

If the substance exists in aqueous state, it is represented by (aq).

If the substance exists in gaseous state, it is represented by (g).

For example:

Evolution of gas

If the gas is liberated in a reaction, it is indicated by an arrow upward

and its physical state is shown by (g).

For example:

Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)↑

Photosynthesis reaction: CO₂ + H₂O C₆H₁₂O₆ + O₂ + H₂O

Balanced equation: 6CO₂ + 12H₂O C₆H₁₂O₆ + 6O₂ + 6H₂O

Step 1: Write the unbalanced equation

CO₂ + H₂O C₆H₁₂O₆ + 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. Thus, first let us consider carbon atom. If we multiply 6 in the reactant (in CO₂), we will get the equal number of atoms as in product (in C₆H₁₂O₆)

Step 4: Write the resulting equation:

6CO₂ + H₂O C₆H₁₂O₆ + O₂ + 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

Hydrogen and oxygen atoms are unequal on the two sides.

first balance the hydrogen atom.

Step 6: If we multiply 12 in the reactant (in H₂O) and 6 in the product (in H₂O), we will get the equal number of hydrogen atoms both sides.

Step 7: Write the resulting equation:

6CO₂ + 12H₂O C₆H₁₂O₆ + O₂ + 6H₂O

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 6 in the product (in O₂), we will get the equal number of atoms as in reactants (in 6CO₂ and 12H₂O)

Step 10: Write the resulting equation:

6CO₂ + 12H₂O C₆H₁₂O₆ + 6O₂ + 6H₂O

We find that the equation is balanced now.

Step 11: Write down the final balanced equation:

6CO₂ + 12H₂O C₆H₁₂O₆ + 6O₂ + 6H₂O

In deserts, the weather is very hot and the amount of rainfall is very low. Hence, if desert plants take CO₂ during day, large amount of water can be lost. To avoid this water loss, some of the desert plants take CO₂ during night.

As you can observe in the above series that zinc is more reactive than the hydrogen whereas copper is less reactive than hydrogen.

More reactive the metal is, more easily it will displace hydrogen atoms. Hence,

i. When zinc reacts with hydrochloric acid, it liberates hydrogen gas (hydrogen is displaced)

Zn + HCl → ZnCl₂ + H₂

ii. On the other hand, when copper reacts with hydrochloric acid, it is unable to displace the hydrogen gas. As a result, no hydrogen gas is liberated.

Cu + HCl → No reaction

Reducing agent: A reducing agent is an element that loses electrons.

The reducing agent means to loose electrons; it is said to have been oxidized.

The element which undergoes oxidation (gets oxidized) is called reducing agent.

a) NH₃ is reducing agent

4NH₃ + 5O₂→ 4NO + 6H₂O

In the given reaction, nitrogen is oxidized to NO by gaining oxygen atom. Thus, NH₃ is reducing agent as it undergoes oxidation.

b) F₂ is reducing agent

H₂O + F₂→ HF + HOF

In the given reaction, F₂ is oxidized to HOF by gaining hydrogen atom. Thus, F₂ is reducing agent as it undergoes oxidation.

(c) CO is reducing agent

Fe₂O₃ + 3CO → 2Fe + 3CO₂

In the given reaction, CO is oxidized to CO₂ by gaining oxygen atom. Thus, CO is reducing agent as it undergoes oxidation.

(d) H₂ is reducing agent

2H₂ + O₂→ 2H₂O

In the given reaction, 2H₂ is oxidized to 2H₂O by gaining oxygen atom. Thus, 2H₂ is reducing agent as it undergoes oxidation.

(a) When copper powder is heated in the presence of air (oxygen), cooper reacts with oxygen to form copper oxide. The copper oxide formed is black in colour. The black colour is formed because the oxidation of copper takes place.

(b) The black substance formed is copper oxide.

(c) The chemical equation of the reaction that takes place is given below:

2Cu + O₂→ 2CuO

Oxidizing agent: An oxidizing agent is an element that gains electrons. Since, the oxidizing agent means to gain electrons; it is said to have been reduced.

The element which undergoes reduction (gets reduced) is called oxidizing agent.

(a) Pb₃O₄ is reducing agent

Pb₃O₄ + 8HCl → 3PbCl₂ + Cl₂ + 4H₂O

In the given reaction, Pb₃O₄ loses oxygen and reduces to PbCl₂.

Thus, Pb₃O₄ is an oxidizing agent as it undergoes reduction.

(b) O₂ is oxidizing agent

2Mg + O₂→ 2MgO

In the given reaction, O₂ is reduced by losing oxygen atoms. Thus, O₂ is an oxidizing agent as it undergoes reduction.

(c) CuSO₄ is oxidizing agent

CuSO₄ + Zn → Cu + ZnSO₄

In the given reaction, CuSO₄ is reduced to Cu by losing oxygen atoms. Thus, CuSO₄ is an oxidizing agent as it undergoes reduction.

(d) V₂O₅ is oxidizing agent

V₂O₅ + 5Ca → 2V + 5CaO

In the given reaction, V₂O₅ is reduced to V by losing oxygen atoms. Thus, V₂O₅ is an oxidizing agent as it undergoes reduction.

(e) H₂O is oxidizing agent

3Fe + 4H₂O → Fe₃O₄ + 4H₂

In the given reaction, H₂O is reduced to H₂ by losing oxygen atoms. Thus, H₂O is an oxidizing agent as it undergoes reduction.

(f) CuO is oxidizing agent

CuO + H₂→ Cu + H₂O

In the given reaction, Cu is reduced to Cu by losing oxygen atom. Thus, CuO is an oxidizing agent as it undergoes reduction.

(a) When nitrogen gas is treated with hydrogen gas in the presence of a catalyst at 773K to form ammonia gas. The following reaction takes place:

The above reaction is a type of combination reaction.

Combination reaction is reaction in which two reactants combined together to form a product.

(b) When sodium hydroxide solution is treated with acetic acid to form sodium acetate and water. The following reaction takes place:

NaOH + CH₃COOH → CH₃COONa + H₂O

The above reaction is a type of neutralization reaction/ double displacement reaction.

A neutralization reaction is a reaction in which base (NaOH) and acid (CH₃COOH) react together to form a salt (CH₃COONa) and water.

(c) When ethanol is warmed with ethanoic acid to form ethyl acetate in presence of conc. H₂SO₄. The following reaction takes place:

The above reaction is a type of esterification reaction/double displacement reaction.

An esterification reaction is a reaction in which alcohol (C₂H₅OH) and Carboxylic acid (CH₃COOH) react together to form a sweet-smelling substance called ester (CH₃COOC₂H₅)

(d) When ethene is burnt in presence of oxygen to form carbon dioxide, water and releases heat and light. The following reaction takes place:

C₂H₄ + 3O₂→ 2CO₂ + 2H₂O + heat + light

The above reaction is a type of combustion reaction.

Combustion reaction is a reaction which takes place in the presence of oxygen to form carbon dioxide.

(a) Pb(NO₃)₂(aq) + 2Kl(aq) → PbI₂(s) + 2KNO₃(aq)

Hence, x is (s) and y is (aq) (s) means PbI₂ exists in solid state and (y) means that KNO₃ exists in aqueous/liquid state.

(b) Cu(s) + 2AgNO₃(aq) → Cu(NO₃)₂(aq) + 2Ag(s)

Hence, x is Ag(s) In the above reaction, Ag gets replaced by Cu.

(c) Zn(s) + H₂SO₄(aq) → ZnSO₄(aq) + H₂(g)

Hence, x is (aq) and y is (g) (aq) means copper sulphate formed exists in aqueous state. (g) means hydrogen gas is liberating.

(d)

Hence x is heat

When CaCO₃ is heated in the presence of oxygen, it forms calcium oxide (CaO) and carbon dioxide.

(a) Double displacement and precipitation reaction

When barium chloride solution is mixed with copper sulphate solution and a white precipitate is observed.

In double displacement reaction, a precipitate is formed which settles down at the bottom. Any reaction that produces a precipitate is calleda precipitation reaction.

BaCl₂ + CuSO₄→ BaSO₄ (↓) + NaCl White ppt.

Note: A precipitate is a substance which is insoluble in water.

(b) Oxidation reaction

On heating copper powder in air in a china dish, the surface of copper powder turns black because copper undergoes oxidation in the presence of air.

2Cu +O₂→ 2CuO Black

(c) Thermal decomposition

On heating green coloured ferrous sulphate crystals, reddish brown solid is left and smell of a gas having odour of burning sulphate is experienced.

In the above reaction, ferrous sulphate (FeSO₄) decomposes to ferric oxide (Fe₂O₃)

(d) Displacement reaction

Iron nails when left dipped in blue copper sulphate solution become brownish in colour and the blue colour of copper sulphate fades away.

Fe + CuSO₄→ FeSO₄ + Cu

As we know that displacement reaction is a reaction in which one element displaces other element from its compound and takes its place there in.

In the above reaction Fe replaces Cu and form a new compound.

(e) Exothermic reaction

Quick lime reacts vigorously with water releasing a large amount of heat:

CaO + H₂O → Ca(OH)₂ + heat

In the above reaction, the heat is released. Hence, it is an exothermic reaction.

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

(a) Sugar is used by athletes because:

i. It is a multipurpose, an all-rounder fruit.

ii. It can be used by athletes as high calorie fruit for high energy.

iii. It increases the flow of blood in the whole body.

iv. It increases haemoglobin too.

(b) We should use sugar apple as a pesticides and insecticides instead of chemicals because:

i. Chemicals can harm plants and can stop their growth.

ii. On the other hand, the powdered seeds of sugar apple do not cause any harm to plants as they are purely natural.

(c) Iron is present in our haemoglobin. Iron is an important element for the formation of blood in the body. The lack of iron in body can cause too many problems. The other fruits which is rich in iron is banana.

(d) People take fruits rich in iron because iron increases the production of blood in the body. It increases the haemoglobin which keeps us fit from top to bottom

(e) Seema is health-conscious, aware and knowledgeable too.