Chapter 9

PARAMOUNT SCHOOL SYSTEM

Subject: Chemistry – I

Unit 9: Chemical Equilibrium

Review Questions

1. Encircle the correct answer.

  1. Which is true about the equilibrium state?

(a) The forward reaction stops.

(b) The reverse reaction stops.

(c) Both forward and reverse reactions stop.

(d) Both forward and reverse reactions continue at the same rate.

  1. When a mixture ​ is sealed in a flask and temperature is kept at 25°C, the following equilibrium is established:

H2​(g) + I2​(g) → 2HI(g)

Which substance is present in the equilibrium mixture?

(a) H2 and I2

(b) HI only

(c) H2​ only

(d) H2 , I2 and HI

  1. Concentration of reactants and products at equilibrium remains unchanged if.

(a) concentration of any reactant or product is not changed.

(b) temperature of the reaction is not changed.

(c) pressure or volume of the system is not changed.

(d) all of the above are observed

  1. Which of the following does not happen when a system is at equilibrium state?

(a) forward and reverse reactions stop.

(b) forward and reverse rates become equal.

(c) concentration of reactants and products stop changing.

(d) reaction continues to occur in both directions.

  1. In an irreversible reaction equilibrium is

(a) established quickly

(b) established slowly

(c) never established

(d) established when reaction stops.

2. Give short answer.

  1. Differentiate between forward and reverse reactions. 
Forward Reaction Reverse Reaction
It is written from left to right. It is written from right to left.
Reactant produce products Products produce reactants.
Initially rate is fastest and gradually slows down. Initially rate is zero and gradually speeds up.
  1. What is chemical equilibrium?

Chemical equilibrium is the state of a reaction where the forward and reverse reactions occur at the same rate. At this point, the concentrations of reactants and products remain constant.

  1. Write two chemical equations of reversible reactions.

Chemical equations of reversible reactions:

  • 2SO2​(g)+O2​(g)

    2SO3​(g)
  • N2​(g)+3H2​(g)

    2NH3​(g)
  1. Write down the conditions for equilibrium.

Conditions for equilibrium are:

  • The concentration of reactant or product remains unchanged.
  • The temperature of the system remains constant.
  • The pressure or volume of the system remains constant.

3. Coal reacts with hot steam to form CO and H2. These substances react further in the presence of a catalyst to give methane and water vapour. 

CO + 3H2 

CH4 + H2O

Write forward and reverse reactions for it.

Forward Reaction:

CO + 3H2  CH4 + H2O

Reverse Reaction:

CH4 + H2O CO + 3H2

4. How does temperature affect cobalt chloride equilibrium?

When hydrated cobalt (II) chloride (a pink solid) is heated, it loses water and becomes anhydrous cobalt (II) chloride (a blue solid), causing the equilibrium to shift to the right. However, when water is added to anhydrous cobalt (II) chloride, it absorbs the water, and the equilibrium shifts to the left, reforming hydrated cobalt (II) chloride.

CoCl2​⋅6H2​O (pink solid)

CoCl2​ (blue solid) + 6H2​O

THINK TANK

1. Bromine chloride (BrCI) decomposes to form chlorine and bromine. Write reversible chemical reaction for this reaction.

The reversible chemical reaction for the decomposition of bromine chloride (BrCl) to form chlorine (Cl₂) and bromine (Br₂) is:

2BrCl

Br2 + Cl2