Unit 9: Chemical Equilibrium

What is Chemical Equilibrium?

Chemical Equilibrium is a fundamental concept in Chemistry that describes the state where the rates of the forward and reverse reactions in a chemical process are equal, leading to no net change in the concentrations of reactants and products. This unit explores the dynamic nature of equilibrium in chemical reactions, the factors that influence it, and how it can be quantitatively described using the equilibrium constant.

Key Topics in Chemical Equilibrium:

• Dynamic Equilibrium: Understanding the balance between the forward and reverse reactions in a closed system.
• Equilibrium Constant (K): Learning how to calculate and interpret the equilibrium constant for different reactions.
• Le Chatelier’s Principle: Exploring how changes in concentration, temperature, and pressure affect the equilibrium position.
• Applications of Equilibrium: Studying real-life examples, such as the Haber process and acid-base reactions.
• Reaction Quotient (Q): Comparing the reaction quotient with the equilibrium constant to predict the direction of a reaction.

Benefits of Studying Chemical Equilibrium:

• Critical Understanding: Provides insights into how chemical reactions are controlled and manipulated in industrial and laboratory settings.
• Problem-Solving Skills: Enhances analytical abilities by solving equilibrium problems involving various factors.
• Practical Applications: Equips students with knowledge that is essential for understanding chemical processes in both academic and professional contexts.

This unit is essential for students to grasp the principles that govern chemical reactions and their outcomes. Mastering Chemical Equilibrium is crucial for success in advanced Chemistry topics and practical applications in scientific fields.

1. The characteristics of reversible reactions are many, except following one

a. products never recombine to form reactants
b. they never complete
c. they proceed in both ways
d. they have a double arrow between reactants and products

2. In the lime kiln , the reaction CaCO3…….. CaO + CO2 goes to completion because

a. of high temperature
b. CaO is more stable than CaCO3
c. CO2 escapes continuously
d. CaO is not dissociated

3. For the reaction 2A + B ……..> 3C the expression for equilibrium constant is

a. [2A][B] / [3C]
b. [A]²[B] / [C]³
c. [3C] / [2A][B]
d. [C]³ / [A]² [B]

4. When a system is at equilibrium state

a. the concentration of reactants and products becomes equal
b. opposing reactions stop
c. rate of reverse reaction becomes very slow
d. rates of forward and reverse reactions become equal

5. Which one of the following statements is not correct about active mass?

a. rate of reaction is directly proportional to active mass
b. active mass is taken in molar concentration
c. active mass is represented by square brackets
d. active mass means total mass of substances

6. When the magnitude of Kc is very large it indicates

a. reaction mixture consists of almost all products
b. reaction mixture consists of almost all reactants
c. reaction has not gone to completion
d. reaction mixture has negligible products

7. When the magnitude of Kc is very small it indicates

a. equilibrium will never establish
b. all reactants will be converted to products
c. reaction will go to completion
d. the amount of products is negligible

8. Reaction which have comparable amounts of reactants and products at equilibrium state have

a. very small Kc value
b. very large Kc value
c. moderate Kc value
d. none of these

9. At dynamic equilibrium

a. reaction stops to proceed
b. amount of reactants and products are equal
c. speed of forward and reverse reactions are equal
d. reaction can no longer be reversed

10. In an irreversible reaction,dynamic equilibrium

a. never establishes
b. establishes before the completion of reaction
c. establishes after the completion of reaction
d. establishes readily

11. A reversible reaction is one:

a. which proceeds from left to right
b. in which reactants react to form products
c. which slows down gradually
d. which speeds up gradually

12. Nitrogen and hydrogen were reacted together to make ammonia. What will be present in the reaction mixture

N2 + 3H2 …………..> 2NH3 Kc=2.86 mol^-2dm⁶

a. NH3 only
b. N2, H2 and NH3
c. N2 and NH3
d. H2 only

13. For a reaction between PCl₃ and Cl₂ to for PCl₅, the units of K_c are

a. mol dm^-3
b. mol^-1 dm^-3
c. mol^-1 dm³
d. mol dm³