10th Class Chemistry notes Short Answers Questions For Getting 100% Marks In Exams

Ans: Life exists on earth due to presence of equilibrium phenomenon taking place in atmosphere. 

Example: A natural process in which we take oxygen and exhale (CO₂) 

Ans: Many environmental systems depend for their existence on delicate equilibrium phenomenon. 

Ans: Substances that combine during a chemical reaction are called Reactants. 

Ans: New substances form in a chemical reaction is called Products. 

Q5: Give an example of reactants and products? Ans: Consider the reaction: 

2H₂ + O₂ 2H₂O 

In above reaction H₂, O₂ are reactants while H₂O is a product. 

Ans: “Those reactions in which products do not recombine to form reactants are called Irreversible reactions.” 

Characteristics: 

(i) These reactions proceed in one direction only. 

(ii) Reactants are completely converted into products. 

(iii) It is represented by a single arrow between the reactants and products. 

Ans: When the rate of forward reaction takes place at the rate of reverse reaction, the composition of the reaction mixture remains constant; it is called Chemical Equilibrium State. 

Q8: Give the Characteristics of Reversible reaction? Ans: Reversible Reaction shows Following Characteristics: – 

(i) Products recombine to form reactants. 

(ii) It proceeds in both ways. 

(iii) Reaction never goes to completion in reversible reaction. 

(iv) It attains the dynamic equilibrium. 

(v) Maximum yield of the products is obtained. 

Ans: If a reversible reaction is allowed to continue for considerable time without changing the conditions and rates of forward reaction and rate of reverse reaction becomes equal but take place in opposite directions this is called dynamic equilibrium. 

Ans: The concentration of specie at equilibrium stage attains the same values whether we start the reaction in the vessel in the forward direction or backward direction. 

Ans: Active mass represents the concentration in mole dm¯³ and it is expressed as square brackets ( ). Rate of reaction is change in concentration of reactant or product divided by the time taken to the change. It is expressed as R=∆c/∆t. So, when active mass of substance change then rate also change. 

Ans: The reaction for synthesis of ammonia is as: 

N₂ + 3H₂ 2NH₃ 

Rf = Kf [N₂][H₂]³ Rr = Kr [NH₃]² 

The expression for equilibrium constant of reaction is: 

Kc = [NH₃]² [N₂][H₂]³ 

(i) H₂ + I₂ ↔2HI 

Ans: Rf = Kf [H₂][I₂] = Rate of forward reaction Rr = Kr [HI]² = Rate of reverse reaction 

Kc = [HI]² = Equilibrium constant expression 

[H₂][I₂] 

(ii) CO + 3H₂ CH₄ + H₂O 

Ans: Rf = Kf [CO][H₂]³ = Rate of forward reaction Rr = Kr [CH₄][H₂O] = Rate of reverse reaction 

Kc = [CH₄][H₂O] = Equilibrium constant expression 

[CO][H₂]³ 

Ans: Direction of chemical reaction at any particular moment can be predict by knowing the numerical values of equilibrium constant of a chemical reaction and comparing this with reaction quotient. 

Ans: If the value of forward becomes equal to reverse the reaction is said to in equilibrium state thus, Qc = Kc such reactions have comparable amounts of reactants and products at equilibrium position. 

(i) The reaction is reversible. 

(ii) Rates of forward and reverse reaction become equal. 

(iii) Amount of reaction and products remains the same. 

(iv) It can be disturbed and achieved again under specific condition. 

Qc Large 

Kc 

Small 

Ans: There are following certain reasons of failure of reaction: 

(i) Reaction is reversible so, products recombine to form reactants and dynamic equilibrium is established. 

(ii) Reaction condition like temperature, pressure and catalyst are not satisfied. 

Ans: When reaction ceases to proceed it is called Static Equilibrium. It occurs in physical phenomenon. 

Example: A building remains standing rather than falling down. 

Ans: As reaction proceed, concentration of reactants decreases with time, so rate of reaction slows down gradually. 

Ans: When number of moles of reactants and products are equal then Kc has no units. 

H₂ + I₂ 2HI 

Kc = [HI]² = (mol.dm¯³)² = No units. [H₂][I₂] (mol.dm¯³)(mol.dm¯³) 

N₂ + 3H₂ 2NH₃ 

Ans:Kc = [NH₃]² = (mol.dm¯³)² = 1 = mol¯²dm⁶ [N₂][H₂]³ (mol.dm¯³)(mol.dm¯³)³ (mol.dm¯³)² 

Ans: It is conventional to write product side in numerator and reactants as denominator. 

Example: N₂ + O₂ 2NO Kc = [NO]² 

[N₂][O₂] 

Q25: Difference Between Forward and Reverse Reaction? 

Ans: 

Forward Reaction 

Reverse Reaction 

(i) In which reactant react to form products. 

In which product react to form reactant. 

(ii) It takes place from left to right. 

It takes place from right to left. 

(iii) It slows down gradually. 

It speedup gradually. 

Ans: Guldberg and waage in 1869 put forward law of mass action. 

Ans: The value of Kᴄ depends only on temperature. It does not depend upon initial concentration of reactants and products. 

Ans: Nitrogen and Oxygen are the major components of atmosphere. 

Ans: It is used to manufacture ammonia which is further used in nitrogenous fertilizer. Example: Urea 

Ans: Oxygen is used to prepare Sulphur dioxide. Sulphur dioxide is used in preparation of Sulphuric acid (H₂SO₄) 

HCl H⁺ + Cl¯ 

Kc = [H⁺][Cl¯] 

[HCl] 

N₂ + O₂ 2NO 

Ans: Rf = Kf [N₂][O₂] = Rate of forward reaction. 

Rf = Kf [NO]² = Rate of reverse reaction. 

Kc = [NO]² = Equilibrium constant expression. 

[N₂][O₂] 

Ans: When substance (reactants) combines to form new substances (products) it is called Chemical Reaction. Reaction and Products are separated by arrow ( ) 

(i) Reversible Reactions. (never complete) 

(ii) Irreversible Reactions. (goes to completion) 

Ans: Ammonia is synthesized by Haber’s process under certain condition of temperature, pressure and catalyst. 

N₂ + 3H₂ 2NH₃ 

Ans: Because products formed in reversible reaction will not escape out in closed vessel. 

Ans: Kf is specific rate constant for forward reaction. While Kr is specific rate constant for reverse reaction. 

Ans: Reaction quotient is [Products] = ratio at any moment of reversible reaction. It is denoted by Qᴄ. 

[Reactants]