Kerala SSLC · Chemistry · Class 10
Rate of Chemical Reactions and Chemical Equilibrium: Important Questions with Answers
These are 10 important multiple-choice questions from the Kerala SSLC Chemistry chapter “Rate of Chemical Reactions and Chemical Equilibrium” (Kerala SCERT syllabus). Each one shows the correct answer and a short explanation of why it is right. Try answering before you read the answer. ExamSummary has 10 practice questions on this chapter in total.
Q1.Which factor increases the rate of reaction primarily by increasing the frequency of effective collisions?
- A)Decreasing temperature
- B)Increasing concentration
- C)Adding inert gas
- D)Decreasing surface area
Answer: B) Increasing concentration
Increasing concentration places more reactant particles in a given volume, leading to more frequent collisions between them. This directly increases the probability of effective collisions occurring per unit time.
Q2.What is the primary function of a catalyst in a chemical reaction?
- A)It shifts the equilibrium position to the right
- B)It increases the activation energy required
- C)It provides an alternative pathway with lower activation energy
- D)It gets consumed permanently during the reaction
Answer: C) It provides an alternative pathway with lower activation energy
A catalyst speeds up the reaction without being consumed by lowering the activation energy barrier through a different mechanism. This allows more molecules to react successfully at the same temperature.
Q3.At chemical equilibrium, which statement is true regarding the rates of forward and reverse reactions?
- A)Forward rate is greater than reverse rate
- B)Reverse rate is greater than forward rate
- C)Both rates become zero
- D)Forward rate equals reverse rate
Answer: D) Forward rate equals reverse rate
At equilibrium, the reaction continues dynamically, meaning the speed of the forward reaction matches the speed of the backward reaction exactly. Therefore, there is no net change in the concentration of reactants or products.
Q4.According to Le Chatelier’s principle, what happens if pressure is increased in a gaseous equilibrium where products have fewer moles?
- A)Equilibrium shifts towards reactants
- B)Equilibrium shifts towards products
- C)No change occurs
- D)Reaction stops immediately
Answer: B) Equilibrium shifts towards products
The system tries to reduce the pressure by shifting to the side with fewer gas molecules, which corresponds to the product side in this case. This minimizes the disturbance caused by the external pressure increase.
Q5.How does temperature affect the equilibrium constant (Keq) for an exothermic reaction?
- A)Keq increases with increase in temperature
- B)Keq decreases with increase in temperature
- C)Keq remains unchanged regardless of temperature
- D)Keq becomes infinite
Answer: B) Keq decreases with increase in temperature
For exothermic reactions, adding heat favors the reverse endothermic direction, thereby reducing the value of the equilibrium constant. Thus, higher temperatures lead to a smaller Keq value.
Q6.In collision theory, why does raising the temperature increase the reaction rate significantly?
- A)It increases the number of particles only
- B)It increases the kinetic energy so more particles exceed activation energy
- C)It changes the nature of the reactants
- D)It decreases the collision frequency
Answer: B) It increases the kinetic energy so more particles exceed activation energy
Higher temperature means particles move faster and collide with more energy, allowing a larger fraction to overcome the activation energy threshold. This results in a higher proportion of successful collisions.
Q7.Which symbol is conventionally used to represent a reversible chemical reaction?
- A)→
- B)⇌
- C)←
- D)≠
Answer: B) ⇌
The double arrow (⇌) indicates that the reaction can proceed in both forward and backward directions simultaneously. This distinguishes reversible reactions from irreversible ones.
Q8.Why is chemical equilibrium described as 'dynamic' rather than static?
- A)Because the concentrations of reactants and products keep changing constantly
- B)Because the macroscopic properties remain constant while microscopic processes continue
- C)Because the reaction eventually stops completely
- D)Because the temperature fluctuates continuously
Answer: B) Because the macroscopic properties remain constant while microscopic processes continue
Although observable properties like concentration stay constant, molecules are still reacting in both directions at equal rates. This continuous activity at the molecular level defines the dynamic nature of equilibrium.
Q9.If a solid reactant is crushed into a fine powder before reacting, how does the rate change?
- A)Rate decreases due to less contact
- B)Rate increases due to increased surface area
- C)Rate remains the same as mass is constant
- D)Rate becomes zero
Answer: B) Rate increases due to increased surface area
Crushing the solid increases its total surface area exposed to other reactants, leading to more frequent collisions per unit time. More exposed particles allow the reaction to proceed faster.
Q10.What is the significance of the equilibrium constant (Kc) being very large (K >> 1)?
- A)Reactants are favored at equilibrium
- B)Products are favored at equilibrium
- C)No reaction takes place
- D)The reaction is irreversible
Answer: B) Products are favored at equilibrium
A large Kc value indicates that the numerator (products) is much larger than the denominator (reactants) at equilibrium. This suggests the reaction proceeds almost to completion.