Tutorial 2 — Chemical Kinetics II

Note: This tutorial PDF consists primarily of scanned images. The questions below are reconstructed based on typical FAD1018 Tutorial 2 content on Chemical Kinetics continuation.

Learning Outcomes

Understand catalysis and catalyst mechanisms
Apply steady-state approximation
Analyze complex reaction mechanisms
Understand enzyme kinetics (Michaelis-Menten)

Part A: Catalysis

Question 1

a) Explain how a catalyst increases the rate of a reaction without being consumed.

b) Distinguish between homogeneous and heterogeneous catalysis with examples.

c) Explain the mechanism of enzyme catalysis using the Michaelis-Menten model.

Question 2

The decomposition of hydrogen peroxide:

$$2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2(g)$$

is catalyzed by iodide ions. The proposed mechanism is:

Step 1: $H_2O_2 + I^- \rightarrow IO^- + H_2O$ (slow) Step 2: $H_2O_2 + IO^- \rightarrow I^- + H_2O + O_2$ (fast)

a) Identify the catalyst.

b) Write the rate law for the reaction.

c) Calculate the activation energy if the rate constants are $1.2 \times 10^{-3}$ s⁻¹ at 20°C and $3.5 \times 10^{-3}$ s⁻¹ at 30°C.

Part B: Reaction Mechanisms

Question 3

For the reaction: $2NO + O_2 \rightarrow 2NO_2$, the following mechanism is proposed:

Step 1: $NO + NO \rightleftharpoons N_2O_2$ (fast equilibrium) Step 2: $N_2O_2 + O_2 \rightarrow 2NO_2$ (slow)

a) Derive the rate law using the steady-state approximation.

b) Show that the rate law is consistent with: Rate = $k[NO]^2[O_2]$.

Part C: Enzyme Kinetics

Question 4

An enzyme-catalyzed reaction follows Michaelis-Menten kinetics with:

$K_M = 4.0 \times 10^{-5}$ M
$V_{max} = 6.0 \times 10^{-8}$ M/s

a) Calculate the reaction rate when $[S] = 2.0 \times 10^{-5}$ M.

b) What substrate concentration is needed to achieve 75% of $V_{max}$?

c) Explain the significance of $K_M$ and $k_{cat}$ in enzyme kinetics.

Part D: Temperature Effects

Question 5

The rate constant for a reaction is $2.5 \times 10^{-4}$ s⁻¹ at 298 K and $7.8 \times 10^{-4}$ s⁻¹ at 308 K.

a) Calculate the activation energy.

b) Predict the rate constant at 318 K.

c) Sketch an energy profile diagram showing the effect of a catalyst.

Key Concepts

Catalyst — Substance that increases reaction rate without being consumed
Homogeneous Catalysis — Catalyst in same phase as reactants
Heterogeneous Catalysis — Catalyst in different phase from reactants
Michaelis-Menten Kinetics — Model for enzyme-catalyzed reactions
Steady-State Approximation — Assumption for reactive intermediates

FAD1018 Tutorial 2 — Chemical Kinetics II