ACS CP Thermodynamics & Chemical Kinetics 3

Question 1

The steady-state approximation in reaction kinetics assumes that:

Accepted Answer

The concentration of reactive intermediates remains approximately constant

Answer

Temperature remains constant during the reaction

Answer

The reaction reaches thermodynamic equilibrium rapidly

Answer

All elementary steps share the same rate constant

Question 2

The Eyring equation from transition state theory expresses the rate constant in terms of:

Accepted Answer

The enthalpy of activation ΔH‡ and entropy of activation ΔS‡

Answer

Only the activation energy barrier Ea

Answer

Only the collision frequency Z

Answer

The equilibrium constant K for the overall reaction

Question 3

For a mechanism with a fast pre-equilibrium step (K₁) followed by a slow rate-determining step (k₂), the observed rate law:

Accepted Answer

May include concentrations from the pre-equilibrium step via K₁

Answer

Contains only concentrations of species in the slow step

Answer

Is always first-order in all reactants

Answer

Is independent of the mechanism chosen

Question 4

The chemical potential (μᵢ) of species i in a mixture is formally defined as:

Accepted Answer

μᵢ = (∂G/∂nᵢ)T,P,nj≠i

Answer

μᵢ = (∂H/∂nᵢ)S,P,nj≠i

Answer

μᵢ = (∂S/∂nᵢ)T,P,nj≠i

Answer

μᵢ = (∂U/∂nᵢ)T,V,nj≠i

Question 5

An autocatalytic reaction where product P catalyzes its own formation from reactant A shows a rate-versus-time curve that is:

Accepted Answer

Sigmoidal (S-shaped)

Answer

Linear from zero throughout the reaction

Answer

Monotonically decreasing from an initial maximum

Answer

Exponentially decaying

Question 6

The Van't Hoff equation d(ln K)/dT = ΔH°/RT² predicts that for an endothermic reaction (ΔH° > 0), increasing temperature will:

Accepted Answer

Increase K because d(ln K)/dT > 0

Answer

Decrease K because the reaction rate slows

Answer

Leave K unchanged since it is only a function of ΔG°

Answer

Decrease K because entropy drives the equilibrium left

Question 7

In collision theory, the Boltzmann factor e^(-Ea/kBT) in the rate constant expression represents:

Accepted Answer

The fraction of molecular collisions possessing energy ≥ Ea

Answer

The average kinetic energy of all molecules in the sample

Answer

The total number of collisions per unit time

Answer

The steric probability factor for correct orientation