Q.1 Which of the following statements is correct for a system in chemical equilibrium?
The concentrations of reactants and products are equal
The rate of forward reaction is equal to the rate of backward reaction
The reaction has stopped completely
The equilibrium constant, K, is always 1
Explanation - At equilibrium, the rate of the forward reaction equals the rate of the backward reaction. Concentrations of reactants and products may not be equal.
Correct answer is: The rate of forward reaction is equal to the rate of backward reaction
Q.2 For the reaction N2 + 3H2 ⇌ 2NH3, what happens to the equilibrium if pressure is increased?
Shifts to the left
Shifts to the right
Remains unchanged
Reaction stops
Explanation - Increasing pressure favors the side with fewer moles of gas. NH3 side has 2 moles vs 4 moles on reactants, so equilibrium shifts right.
Correct answer is: Shifts to the right
Q.3 Which of the following reactions has the largest equilibrium constant (K) at room temperature?
H2 + I2 ⇌ 2HI
N2 + 3H2 ⇌ 2NH3
CO + Cl2 ⇌ COCl2
H2 + Cl2 ⇌ 2HCl
Explanation - H2 + Cl2 ⇌ 2HCl is highly exothermic and nearly complete, giving a very large K at room temperature.
Correct answer is: H2 + Cl2 ⇌ 2HCl
Q.4 Le Chatelier's principle predicts that when a reactant is added to a system at equilibrium:
Equilibrium shifts toward reactants
Equilibrium shifts toward products
Reaction stops
No change occurs
Explanation - Adding more reactant disturbs equilibrium; the system shifts toward products to counteract the change.
Correct answer is: Equilibrium shifts toward products
Q.5 The value of the equilibrium constant K depends on:
Concentrations of reactants and products
Temperature
Catalyst
Time
Explanation - K depends only on temperature. Catalysts speed up attainment of equilibrium but do not affect K.
Correct answer is: Temperature
Q.6 For the reaction PCl5 ⇌ PCl3 + Cl2, Kc = 0.1 at a certain temperature. This means:
Products are favored
Reactants are favored
Equal amounts of reactants and products
Reaction is at standard state
Explanation - Kc < 1 means reactants are favored at equilibrium.
Correct answer is: Reactants are favored
Q.7 Which of the following will NOT affect the equilibrium constant K for a reaction?
Addition of a catalyst
Change in temperature
Change in pressure for gaseous reactions
Change in concentration of reactants
Explanation - Catalysts accelerate the rate of both forward and backward reactions equally but do not change K.
Correct answer is: Addition of a catalyst
Q.8 If ΔG° for a reaction is negative, the equilibrium constant K:
K > 1
K < 1
K = 0
K = 1
Explanation - ΔG° < 0 indicates a spontaneous reaction under standard conditions; hence K > 1 favoring products.
Correct answer is: K > 1
Q.9 For the reaction 2SO2 + O2 ⇌ 2SO3, what is the effect of increasing temperature?
Shifts equilibrium to the right
Shifts equilibrium to the left
No effect
Equilibrium constant increases
Explanation - Formation of SO3 is exothermic; increasing temperature shifts equilibrium toward reactants (endothermic direction).
Correct answer is: Shifts equilibrium to the left
Q.10 The equilibrium constant expression for aA + bB ⇌ cC + dD is:
K = [A]^a [B]^b / [C]^c [D]^d
K = [C]^c [D]^d / [A]^a [B]^b
K = [C][D] / [A][B]
K = [A]^c [B]^d / [C]^a [D]^b
Explanation - K = products^coefficients / reactants^coefficients, as per the law of mass action.
Correct answer is: K = [C]^c [D]^d / [A]^a [B]^b
Q.11 Which reaction shows dynamic equilibrium?
Ice melting in a freezer
N2 + 3H2 ⇌ 2NH3 in a closed vessel
Rusting of iron
Combustion of methane
Explanation - Dynamic equilibrium occurs when forward and backward reactions occur at equal rates; the NH3 synthesis is reversible.
Correct answer is: N2 + 3H2 ⇌ 2NH3 in a closed vessel
Q.12 If Q < K for a reaction, the system will:
Shift toward reactants
Shift toward products
Be at equilibrium
Reaction stops
Explanation - Q is the reaction quotient. If Q < K, more products will form to reach equilibrium.
Correct answer is: Shift toward products
Q.13 For the reaction H2 + I2 ⇌ 2HI, the rate of formation of HI at equilibrium is:
Zero
Equal to the rate of decomposition of HI
Maximum
Minimum
Explanation - At equilibrium, the forward and backward rates are equal, so the rate of formation of HI equals the rate of its decomposition.
Correct answer is: Equal to the rate of decomposition of HI
Q.14 Which factor would increase the rate of attainment of equilibrium but not change its position?
Adding a catalyst
Increasing concentration of reactants
Increasing temperature
Decreasing pressure
Explanation - Catalysts speed up reactions but do not affect equilibrium composition or K.
Correct answer is: Adding a catalyst
Q.15 The Haber process is an example of:
Dynamic equilibrium
Static equilibrium
Irreversible reaction
Physical equilibrium
Explanation - Haber process involves reversible reactions where forward and backward rates are equal at equilibrium, making it dynamic.
Correct answer is: Dynamic equilibrium
Q.16 Which of the following reactions is endothermic in the forward direction?
N2 + 3H2 ⇌ 2NH3
CaCO3 ⇌ CaO + CO2
2SO2 + O2 ⇌ 2SO3
H2 + Cl2 ⇌ 2HCl
Explanation - Decomposition of CaCO3 absorbs heat, making the forward reaction endothermic.
Correct answer is: CaCO3 ⇌ CaO + CO2
Q.17 Which of the following is true for Kp and Kc for a gaseous reaction?
Kp = Kc always
Kp = Kc(RT)^Δn
Kp > Kc always
Kp < Kc always
Explanation - For gaseous reactions, Kp = Kc(RT)^Δn where Δn = moles of gaseous products - moles of gaseous reactants.
Correct answer is: Kp = Kc(RT)^Δn
Q.18 For the reaction 2A ⇌ B, if K = 4, and initially [A] = 1 M, [B] = 0, the equilibrium concentration of B will be:
0.5 M
0.8 M
0.67 M
1 M
Explanation - Let x = [B] at equilibrium, then [A] = 1 - x/2. K = [B]/[A]^2 = x/(1 - x/2)^2 = 4 → solving gives x ≈ 0.67 M.
Correct answer is: 0.67 M
Q.19 Which of the following is TRUE about heterogeneous equilibrium?
Concentration of solids is included in K expression
Concentration of solids and liquids are constant
It cannot be represented by K
It is only physical equilibrium
Explanation - In heterogeneous equilibrium, concentrations of pure solids and liquids do not change and are omitted from the K expression.
Correct answer is: Concentration of solids and liquids are constant
Q.20 Which of the following reactions is shifted to the left when temperature increases?
N2 + 3H2 ⇌ 2NH3
CaCO3 ⇌ CaO + CO2
H2 + I2 ⇌ 2HI
CO + Cl2 ⇌ COCl2
Explanation - The forward reaction in Haber process is exothermic. Increasing temperature favors the endothermic reverse reaction (left shift).
Correct answer is: N2 + 3H2 ⇌ 2NH3
Q.21 What is the effect of adding an inert gas at constant volume on equilibrium?
Shifts equilibrium toward products
Shifts equilibrium toward reactants
No effect
Increases rate of reaction
Explanation - Adding inert gas at constant volume does not change partial pressures of reactants or products, so equilibrium remains unchanged.
Correct answer is: No effect
Q.22 The value of Kc for the reaction 2SO2 + O2 ⇌ 2SO3 decreases with temperature. This indicates:
Reaction is exothermic
Reaction is endothermic
Catalyst is present
Pressure is increasing
Explanation - Decrease in K with temperature indicates exothermic forward reaction, as per Le Chatelier's principle.
Correct answer is: Reaction is exothermic
Q.23 Which of the following statements about equilibrium is FALSE?
Equilibrium can be dynamic
Equilibrium can be static
Equilibrium constant changes with catalyst
Equilibrium depends on temperature
Explanation - Catalysts do not change equilibrium constant; they only speed up the attainment of equilibrium.
Correct answer is: Equilibrium constant changes with catalyst
Q.24 For the reaction A ⇌ B, the half-life of A at equilibrium is:
Infinite
Zero
Finite and constant
Dependent on rate constant
Explanation - At equilibrium, concentrations remain constant, but the reaction is dynamic; the concept of half-life applies to rates, not equilibrium directly.
Correct answer is: Finite and constant
Q.25 Which of the following will shift the equilibrium of exothermic reaction to the right?
Increasing temperature
Decreasing temperature
Adding inert gas at constant volume
Removing a catalyst
Explanation - Lowering temperature favors exothermic forward reaction, shifting equilibrium to the right.
Correct answer is: Decreasing temperature
Q.26 For a reaction at equilibrium, the reaction quotient Q is found to be equal to K. This means:
Reaction will proceed forward
Reaction will proceed backward
System is at equilibrium
Reaction is not allowed
Explanation - When Q = K, the system is at equilibrium; no net change occurs.
Correct answer is: System is at equilibrium