Unit 11: Reaction Kinetics

31. In a reaction mechanism, the species that is formed in one step and consumed in a subsequent step is called:

a) A catalyst
b) An intermediate
c) A reactant
d) A product
Answer: b) An intermediate

32. The slowest step in a reaction mechanism is known as:

a) The fast step
b) The intermediate step
c) The rate-determining step
d) The equilibrium step
Answer: c) The rate-determining step

33. The rate of a reaction is expressed as:

a) The rate of formation of products
b) The rate of disappearance of reactants
c) The rate of consumption of reactants
d) All of the above
Answer: d) All of the above

34. The term “pseudo-steady-state approximation” is often used in the study of:

a) Zero-order reactions
b) First-order reactions
c) Multi-step reaction mechanisms
d) Single-step reactions
Answer: c) Multi-step reaction mechanisms

35. The rate of a reaction is proportional to the concentration of reactants raised to a power known as:

a) The reaction quotient
b) The reaction order
c) The activation energy
d) The rate constant
Answer: b) The reaction order

36. The method used to determine the order of a reaction with respect to each reactant is:

a) Method of initial rates
b) Method of half-life
c) Method of integrated rates
d) Method of activation energy
Answer: a) Method of initial rates

37. The half-life of a first-order reaction is:

a) Directly proportional to the initial concentration of reactants
b) Inversely proportional to the initial concentration of reactants
c) Independent of the initial concentration of reactants
d) Dependent on the temperature of the reaction
Answer: c) Independent of the initial concentration of reactants

38. The unit of the rate constant for a second-order reaction is:

a) M/s
b) M⁻¹s⁻¹
c) M²s⁻¹
d) s⁻¹
Answer: b) M⁻¹s⁻¹

39. The term “reaction rate” refers to:

a) The speed at which the reactants are consumed
b) The speed at which products are formed
c) The change in concentration of reactants or products over time
d) All of the above
Answer: d) All of the above

40. The reaction rate increases as the temperature is raised because:

a) The activation energy decreases
b) The frequency of collisions decreases
c) The number of collisions with sufficient energy increases
d) The concentration of reactants decreases
Answer: c) The number of collisions with sufficient energy increases