Q.1 Which of the following is true for a system in dynamic 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
Only the reactants are present
Explanation - At dynamic equilibrium, the forward and backward reactions continue at equal rates, so the concentrations remain constant but are not necessarily equal.
Correct answer is: The rate of forward reaction is equal to the rate of backward reaction
Q.2 Le Chatelier’s principle is used to predict the effect of which factor on equilibrium?
Temperature, pressure, and concentration
Molecular weight of reactants
Type of catalyst only
Solubility of reactants in water
Explanation - Le Chatelier’s principle states that if a system at equilibrium is disturbed by a change in concentration, temperature, or pressure, the system shifts to counteract the disturbance.
Correct answer is: Temperature, pressure, and concentration
Q.3 For the reaction N2(g) + 3H2(g) ⇌ 2NH3(g), what will happen if pressure is increased?
Equilibrium will shift to the left
Equilibrium will shift to the right
Equilibrium remains unchanged
Reaction stops
Explanation - Increasing pressure favors the side with fewer gas molecules. Here, 4 molecules of reactants produce 2 molecules of product, so equilibrium shifts right.
Correct answer is: Equilibrium will shift to the right
Q.4 Which expression represents the equilibrium constant Kc for aA + bB ⇌ cC + dD?
Kc = [A]^a[B]^b / [C]^c[D]^d
Kc = [C]^c[D]^d / [A]^a[B]^b
Kc = [A][B] / [C][D]
Kc = [C]^a[D]^b / [A]^c[B]^d
Explanation - The equilibrium constant Kc is the ratio of product concentrations to reactant concentrations, each raised to the power of their stoichiometric coefficients.
Correct answer is: Kc = [C]^c[D]^d / [A]^a[B]^b
Q.5 Which of the following is NOT affected by a catalyst in an equilibrium reaction?
Rate of forward reaction
Rate of backward reaction
Position of equilibrium
Activation energy
Explanation - A catalyst speeds up both forward and backward reactions equally but does not change the equilibrium position or the concentrations of reactants/products at equilibrium.
Correct answer is: Position of equilibrium
Q.6 The value of Kc for an exothermic reaction decreases with:
Increase in temperature
Decrease in temperature
Increase in pressure
Addition of catalyst
Explanation - For an exothermic reaction, increasing temperature shifts equilibrium backward (towards reactants), decreasing Kc.
Correct answer is: Increase in temperature
Q.7 Which statement correctly describes heterogeneous equilibrium?
All reactants and products are in the same phase
Reactants and products are in different phases
Equilibrium constant Kc is zero
Reaction cannot reach equilibrium
Explanation - Heterogeneous equilibrium involves reactants and products in different phases, e.g., solid and gas.
Correct answer is: Reactants and products are in different phases
Q.8 For the reaction 2SO2(g) + O2(g) ⇌ 2SO3(g), increasing temperature favors:
Formation of SO3
Formation of SO2 and O2
No effect
Reaction stops
Explanation - The reaction is exothermic; increasing temperature shifts equilibrium toward reactants according to Le Chatelier's principle.
Correct answer is: Formation of SO2 and O2
Q.9 In the Haber process, which factor is kept low to favor high rate of reaction?
Temperature
Pressure
Catalyst amount
Nitrogen concentration
Explanation - Low temperature favors formation of ammonia (exothermic), but too low temperature decreases reaction rate; hence moderate temperature is used industrially.
Correct answer is: Temperature
Q.10 Which of the following reactions will have the largest Kc value?
H2 + I2 ⇌ 2HI
N2 + 3H2 ⇌ 2NH3
CO + Cl2 ⇌ COCl2
CH4 + 2O2 ⇌ CO2 + 2H2O
Explanation - Reaction forming products almost completely has a very large Kc; combustion reactions generally have very large equilibrium constants.
Correct answer is: CH4 + 2O2 ⇌ CO2 + 2H2O
Q.11 If the equilibrium constant Kc = 1, what can be inferred about the equilibrium?
Products are favored
Reactants are favored
Neither reactants nor products are favored
Reaction does not occur
Explanation - Kc = 1 indicates comparable concentrations of reactants and products at equilibrium.
Correct answer is: Neither reactants nor products are favored
Q.12 For the reaction A ⇌ B, the addition of inert gas at constant volume:
Shifts equilibrium to the right
Shifts equilibrium to the left
Has no effect on equilibrium
Increases Kc
Explanation - Adding an inert gas at constant volume does not change the partial pressures of reactants or products, so equilibrium remains unchanged.
Correct answer is: Has no effect on equilibrium
Q.13 Which type of reaction has Kp = Kc(RT)^Δn?
Homogeneous gas reactions
Heterogeneous reactions
Reactions in solution
Precipitation reactions
Explanation - For gaseous reactions, Kp is related to Kc through Δn = moles of gaseous products − moles of gaseous reactants.
Correct answer is: Homogeneous gas reactions
Q.14 The equilibrium constant for the reaction 2NO2 ⇌ N2O4 at 298 K is 0.143. This indicates that:
Reaction favors products
Reaction favors reactants
System is at standard conditions
Reaction does not occur
Explanation - Kc < 1 indicates reactants are favored at equilibrium.
Correct answer is: Reaction favors reactants
Q.15 In the reaction H2(g) + Cl2(g) ⇌ 2HCl(g), the effect of increasing Cl2 concentration is:
Shifts equilibrium to left
Shifts equilibrium to right
Decreases rate of forward reaction
No change in equilibrium
Explanation - According to Le Chatelier’s principle, increasing reactant concentration shifts equilibrium toward products.
Correct answer is: Shifts equilibrium to right
Q.16 Which of the following is true for a reaction with K >> 1?
Reaction favors products
Reaction favors reactants
Equilibrium constant is negligible
Reaction is incomplete
Explanation - A large K indicates that at equilibrium, products predominate over reactants.
Correct answer is: Reaction favors products
Q.17 In the dissociation of PCl5 ⇌ PCl3 + Cl2, if volume is doubled, the equilibrium:
Shifts right
Shifts left
Remains unchanged
Reaction stops
Explanation - Doubling volume decreases pressure; equilibrium shifts to the side with more gas molecules (right side) to counteract the change.
Correct answer is: Shifts right
Q.18 Which factor does NOT affect the equilibrium constant Kc?
Temperature
Pressure
Catalyst
Concentration of reactants
Explanation - Catalysts affect the rate of reaction but do not change the value of equilibrium constant.
Correct answer is: Catalyst
Q.19 For the reaction CO(g) + 2H2(g) ⇌ CH3OH(g), the reaction is exothermic. What happens if temperature decreases?
Equilibrium shifts to products
Equilibrium shifts to reactants
Equilibrium remains unchanged
Kc decreases
Explanation - Decreasing temperature favors the exothermic direction (forward reaction) to produce more CH3OH.
Correct answer is: Equilibrium shifts to products
Q.20 If Q < K for a reaction, the reaction will:
Shift to left
Shift to right
Remain at equilibrium
Stop immediately
Explanation - Q is the reaction quotient; if Q < K, more products need to form to reach equilibrium, so reaction shifts right.
Correct answer is: Shift to right
Q.21 The reaction 2SO3(g) ⇌ 2SO2(g) + O2(g) is endothermic. Adding heat:
Shifts equilibrium left
Shifts equilibrium right
No effect
Decreases Kc
Explanation - For an endothermic reaction, heat acts as a reactant; increasing temperature shifts equilibrium toward products.
Correct answer is: Shifts equilibrium right
Q.22 Which of the following is a characteristic of a reaction at equilibrium?
Forward reaction stops
Backward reaction stops
Forward and backward reaction rates are equal
Concentration of reactants becomes zero
Explanation - At equilibrium, both forward and backward reactions continue at equal rates; concentrations remain constant.
Correct answer is: Forward and backward reaction rates are equal
Q.23 Which statement about Kc and Kp is correct?
Kc is for gases only
Kp is for solutions only
Kc and Kp can be related using Δn
Kc always equals Kp
Explanation - Kp and Kc for gaseous reactions are related by Kp = Kc(RT)^Δn, where Δn = moles of gaseous products − moles of gaseous reactants.
Correct answer is: Kc and Kp can be related using Δn
Q.24 For the equilibrium reaction 2A ⇌ B, if initially only A is present, the reaction:
Shifts left
Shifts right until equilibrium is reached
Remains unchanged
Reaches Kc = 0
Explanation - Starting with only reactants, the reaction shifts right to form products until equilibrium is established.
Correct answer is: Shifts right until equilibrium is reached
Q.25 The value of Kc for a reaction is independent of:
Temperature
Concentration of reactants
Pressure
All of the above
Explanation - Kc depends only on temperature; changing reactant concentrations does not alter the equilibrium constant.
Correct answer is: Concentration of reactants