Very Short Answer Type Questions
Question 1. What is meant by equilibrium?
Answer: Equilibrium is a state at which rate of forwarding reaction is equal to the rate of backward reaction.
Question 2. State the law of mass action?
Answer: It states that the rate at which a substance reacts is directly proportional to its molar concentration.
Question 3. What is meant by reaction quotient?
Answer: It is defined as the ratio of the product of molar concentration of products to the product of molar concentration of reactants at any stage of the reaction.
Question 4. Define ionic equilibrium.
Answer: The equilibrium between ions and unionised molecules is called ionic equilibrium.
Question 5. What is meant by ionic product of water (kw)?
Answer: It is the product of concentration of [ H3O+] and [OH–] at a specific temperature.
Kw = [H3O+] [OH–]
= 1.0 x 10-14 at 298 K
Question 6. Define solubility product.
Answer: It is product of molar concentration of ion raised to the power of number of ions produced per compound in saturated solution.
Question 7. How does common ion affect the solubility of electrolyte?
Answer: Solubility of electrolyte decreases due to common ion effect.
Question 8. Write conjugate add and conjugate base of H2O?
Answer: Conjugate acid is H3O+ and conjugate base is OH–.
Question 9. Give two characteristics of a buffer solution.
- Its pH does not change on the addition of small amount of acid or base.
- Its pH does not change on dilution or standing.
Question 10. How does a catalyst affect the equilibrium constant?
Answer: The equilibrium constant is not affected by a catalyst.
Question 11. State Ostwald’s dilution law.
Answer: Ostwald’s dilution law states that the degree of dissociation of weak electrolyte is inversely proportional to square root of its concentration.
Where, Kfl and Kfc are acid dissociation and base dissociation constants.
Question 12. What is basic buffer?
Answer: Basic buffer is the buffer whose pH is more than 7. It is a mixture containing weak base and its salt with a strong acid, e.g., NH4Cl + NH4OH
Question 13. S032-is Bronsted base or acid and why?
Answer: S032-is Bronsted base because it can accept H+.
What is the relationship between Kp and Kc?
Answer: Kp = Kc
because ∆n = 0.
Question 15. Define common ion effect.
Answer: The supervision in concentration of one of the ions by adding other ion as common ion is called common ion effect.
Short Answer Type Questions
Question 1. The following concentration were obtained for the formation of NH3 from N2 and H2 at equilibrium at 500 K.[N2(g)] = 1.5 x 10-2 M [H2 (g)] = 3.0 x 10-2 M [NH3] = 1.2 x 10-2 M. Calculate equilibrium constant.
Question 2. Write the equilibrium constant (Kc) expression for the following reactions.
Question 3. Given the equilibrium N2O4 (g) ——->2NO2 (g) K=0.15 atm at 298 K
- (a) What is Kp using pressure in torr?
- (b) What is Kc using units of moles per litre.
Question 4. In the reaction A + B———> C + D, what will happen to the equilibrium if concentration of A is increased?
- (b) The equilibrium constant for a reaction is 2 x 10-23 at 25°C and 2 x 10-2 at 50°C. Is the reaction endothermic or exothermic?
- (c) Mention at least three ways by which the concentration of S03 can be increased in the following reaction in a state of equilibrium.
(a) The reaction will shift in the forward direction.
(c) (i) lowering the temperature (ii) increasing pressure.
(iii) increasing concentration of oxygen.
Question 5. (i) Define Le Chatelier’s principle.
(ii) Following reactions occur in a Blast furnace.
Fe203(s) + 3CO(g) ———–>2Fe(s) + 3CO2(g)
use Le chatelier’s principle to predict the direction of reaction when equilibrium mixture is disturbed by
(a) adding Fe203 (b) removing CO2 .
(c) removing CO.
(a) When a system under equilibrium is subjected to a change in temperature, pressure or concentration, then the equilibrium shifts in such a direction so as to undo the effect of the change.
(ii) (a) On adding Fe203(s), the equilibrium will remain unaffected.
(b) By removing CO2 (g), the equilibrium will be shifted in the forward direction.
(c) By removing CO(g), the equilibrium will be shifted in the backward direction.
Long Answer Type Questions
(i) Point out the differences between ionic product and solubility product.
(ii) The solubility of AgCl in water at 298 K is 1.06 x 10-5 mole per litre. Calculate its solubility product at this temperature.
Question 2. At certain temperature and under a pressure of 4 atm, PCl5 is 10% dissociated. Calculate the pressure at which PCl5 will be 20% dissociated at temperature remaining constant.
Answer: Calculation of Kp
Question 1. For the equilibrium 2 NOCl(g)——-> 2NO(g) + Cl2(g) the value of the equilibrium constant Kc is 3.75 x 10-6 at 1069 K. Calculate the Kp for the reaction at this temperature?
Answer: We know that Kp = Kc(RT)∆n
For the above reaction, ∆n = (2 + 1) – 2 = 1 Kp = 3.75 x 10’6 (0.0831 x 1069)
Kp = 0.033.
Question 2. The values of Ksp of two sparingly soluble salts Ni(OH)2 and AgCN are 2.0 x 10-15 and 6 x 10-17 respectively. Which salt is more soluble? Explain.
Question 3. The value of Kc for the reaction 2A——>B + C is 2 x 10-3. At a given time, the composition of reaction mixture is [A] = [B] = [C] = 3 x 10-4 M. In which direction the reaction will proceed?
For the reaction the reaction quotient Qc is given by Qc = [B] [C]/[A]2 as [A] = [B] = [C] = 3 x 10-4 M Qc = (3 x 10-4) (3 x10-3)/(3 x 10) = 1
as Qc > Kc, so, the reaction will proceed in the reverse direction.
Question 4. PCl5, PCl3 and Cl2 are at equilibrium at 500 K and having concentration 1.59M PCl5 1.59M Cl2 and 1.41M PCl5. Calculate Kc for the reaction PCl5———>PC13+ Cl2
Answer: The equilibrium constant Kc for the above reaction can be written as:
Question 5. Dihydrogen gas is obtained from natural gas by partial oxidation with steam as per following endothermic reaction:
CH4(g) + H2O(g) ——> CO(g) + 3 H2(g)
- (a) Write an expression for Kpfor the above reaction.
- (b) How will the values of Kp and composition of equilibrium mixture be affected by
- (i) increasing the pressure
- (ii) increasing the temperature
- (iii) using a catalyst?
(b) (i) value of Kp will not change, equilibrium will shift in backward direction.
(ii) value of Kp will increase and reaction will proceed in forward direction.
(iii) no effect.