Reaction Kinetics MCQs for MDCAT Practice

Chemistry section, Reaction Kinetics chapter. Up to eight free sample questions, each with the correct answer and a worked explanation. The full chapter opens in the app.

1. Question 1
   The branch of Chemistry that deals with the reactions rates and reaction mechanism is called:
   • AChemical Kinetics (correct answer)
   • BThermodynamics
   • CPhotochemistry
   • DAnalytical Chemistry
   Correct answer: A

   This question tests your understanding of the fundamental branches of chemistry, specifically identifying the field that studies reaction rates and mechanisms.
2. Question 2
   The specific rate constant of a chemical reaction is the rate of the reaction when the concentration of the reactant is
   • ALess than unity
   • BEqual to unity (correct answer)
   • CGreater than unity
   • DEqual to the concentration of 2nd order reaction
   Correct answer: B

   The specific rate constant (k) represents the reaction rate when reactant concentrations are standardized to unity (1 M), independent of reaction order.
3. Question 3
   A substance that alters the rate of chemical reaction without being consumed in the reaction is called:
   • ACatalyst (correct answer)
   • BReactant
   • CProduct
   • DActivated complex
   Correct answer: A

   This question tests the definition of a catalyst, a substance that speeds up or slows down a reaction without being consumed.
4. Question 4
   Which of the following increases the rate of reaction?
   • ADecrease temp
   • BDecrease conc.
   • CIncrease surface area (correct answer)
   • DAdd inhibitor
   Correct answer: C

   Boosting reaction rate hinges on increasing effective collisions. Higher surface area, temperature, and concentration facilitate this; inhibitors do the opposite.
5. Question 5
   The sum of all the exponents (power) of the reactants in the rate expression is called:
   • AMolecularity
   • BAtomicity of the molecules
   • COrder of reaction (correct answer)
   • DNone of the above
   Correct answer: C

   The order of reaction is defined as the sum of the exponents of reactant concentrations in the rate law, distinguishing it from molecularity.
6. Question 6
   If the graphic representation of the energy levels of the reactants and products in a chemical reaction looks like this: Which of the following statements are true? I. The activation energy for the forward reaction is represented by the “a” portion. II. The activation energy for the forward reaction is represented by the “b” portion of the graph. III. The “a” portion is the energy given off in the forward reaction.
   
   • AII only
   • BI and III only
   • CII and III only
   • DI only (correct answer)
   Correct answer: D

   This question tests understanding of activation energy and enthalpy change from a reaction energy profile diagram.
7. Question 7
   What is detailed sequence of steps that leads to the net overall reaction called?
   • AReaction coordinate
   • BReaction mechanism (correct answer)
   • CReaction potential
   • DReaction rate law
   Correct answer: B

   The sequence of elementary steps constituting a chemical reaction is termed the reaction mechanism.
8. Question 8
   In the termination step where two methyl radicals combine to form ethane (CH3. + .CH3 -> C2H6), the reaction typically has an activation energy of approximately zero. What is the logical reason for this?
   • AThe entropy of the universe decreases significantly.
   • BThere are no bonds to break and two open-shell electrons are pairing. (correct answer)
   • CThe reaction is endothermic.
   • DMethyl radicals are stable species that drift together slowly.
   Correct answer: B

   Radical recombination reactions have near-zero activation energy because they involve simple electron pairing without bond breaking, making them highly favorable.

Read the full Reaction Kinetics chapter notes: Reaction Kinetics notes. Or browse every chapter.