S.C.O.R.E: Chemical Catalytic Reaction

What is the primary function of a catalyst in a chemical reaction?

• • A) It lowers the temperature of the reaction.

• • B) It changes the equilibrium position of the reaction.

• • C) It lowers the activation energy of the reaction.

• • D) It is consumed in the reaction to form products.

Answer explanation

Explanation: A catalyst speeds up a reaction by providing an alternative pathway with lower activation energy. It does not affect the equilibrium or get consumed in the reaction.

Which of the following is NOT a step in a heterogeneous catalytic reaction?

• • A) Adsorption of reactants onto the catalyst surface.

• • B) Chemical reaction on the catalyst surface.

• • C) Desorption of products from the catalyst surface.

• • D) Dissolution of the catalyst into the reaction medium.

Answer explanation

Explanation: In heterogeneous catalysis, the catalyst remains in a separate phase (usually solid) from the reactants and products. Dissolution of the catalyst is not a step in this process.

Why is identifying the rate-limiting step important in postulating the overall rate equation for a chemical catalytic reaction?

• • A) It helps to simplify the reaction mechanism by ignoring all other steps.

• • B) It determines the temperature at which the reaction should occur.

• • C) It directly controls the overall reaction rate, which the rate equation is based on.

• • D) It eliminates the need for understanding intermediate reaction steps

Answer explanation

Explanation: The rate-limiting step is the slowest step in a reaction mechanism, and thus it determines the overall reaction rate. The rate equation is typically derived based on this step, as it dictates how the concentrations of reactants affect the reaction rate.

How does the rate-limiting step influence the form of the rate law or rate expression in catalytic reactions?

• • A) The rate law is determined by the fastest step in the mechanism.

• • B) The rate-limiting step dictates which reactants appear in the rate law.

• • C) The rate law is independent of the rate-limiting step.

• • D) The rate-limiting step determines only the catalyst's activity.

Answer explanation

Explanation: The reactants involved in the rate-limiting step are included in the rate law because this step determines the overall reaction speed. The concentration of these reactants will affect the reaction rate as described by the rate law.

When designing a catalytic reactor, which of the following is NOT typically a consideration?

• • A) Reaction kinetics.

• • B) Heat and mass transfer.

• • C) Catalyst deactivation.

• • D) The solubility of the catalyst.

Answer explanation

Explanation: Since catalytic reactions are often heterogeneous (with the catalyst in a solid phase and reactants in gas or liquid phases), the solubility of the catalyst is not a concern. However, kinetics, heat/mass transfer, and catalyst deactivation are critical factors.

Which of the following is a common cause of catalyst deactivation?

• • A) Adsorption of reactants onto the catalyst surface.

• • B) The reaction rate increases too quickly.

• • C) Sintering of catalyst particles.

• • D) Desorption of products from the catalyst surface.

Answer explanation

Explanation: Sintering occurs when catalyst particles agglomerate at high temperatures, reducing the available surface area for the reaction. This is a common cause of catalyst deactivation. Adsorption and desorption are normal steps in catalysis and do not deactivate the catalyst.

What could happen to a catalyst if the reaction temperature is too high?

• • A) The catalyst will speed up the reaction indefinitely.

• • B) The catalyst will sinter, losing active surface area.

• • C) The catalyst will become more efficient over time.

• • D) The catalyst will dissolve into the reaction medium.

Answer explanation

Explanation: Excessive heat can cause sintering, where the catalyst particles fuse together, reducing the effective surface area for catalysis and decreasing its activity.

Catalyst poisoning refers to:

• • A) The increase in catalytic activity over time.

• • B) The rapid production of unwanted by-products.

• • C) The deactivation of the catalyst due to irreversible adsorption of impurities.

• • D) The dissolution of the catalyst into the reaction mixture.

Answer explanation

Explanation: Catalyst poisoning occurs when impurities in the reaction mixture bind strongly to active sites on the catalyst, preventing the desired reaction from occurring. This reduces the efficiency of the catalyst.

SELF-ASSESSMENT

How confident are you in explaining the role of a catalyst in a chemical reaction?

• • A) Very confident – I can clearly explain how catalysts provide an alternative reaction pathway and lower activation energy.

• • B) Somewhat confident – I understand the basic idea but struggle with some details.

• • C) Not very confident – I need to review how catalysts work in reactions.

• • D) Not confident at all – I do not understand the concept of catalysts.

SELF-ASSESSMENT

How well do you understand the concept of the rate-limiting step in a catalytic reaction?

• • A) Very well – I can identify and explain how the rate-limiting step controls the overall reaction rate.

• • B) Somewhat – I know the importance of the rate-limiting step but may have difficulty applying it.

• • C) Not well – I find it hard to determine which step is rate-limiting in complex reactions.

• • D) Not at all – I am unsure what the rate-limiting step is and why it matters.