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

The steady-state approximation assumes reactive intermediates are formed and consumed at equal rates, keeping their concentrations approximately 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

The Eyring equation k = (kBT/h)·e^(ΔS‡/R)·e^(-ΔH‡/RT) expresses k using both enthalpic and entropic activation parameters at the transition state.

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

The equilibrium constant K₁ for the fast step relates intermediate concentrations to reactant concentrations, which then appear in the observed rate law.

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

Chemical potential is the partial molar Gibbs free energy: μᵢ = (∂G/∂nᵢ) at constant T, P, and amounts of all other species.

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

Autocatalytic reactions produce sigmoidal curves: initially slow (little catalyst P), then accelerating as P accumulates, then slowing as A depletes.

(ACS CP) American Chemical Society (ACS) Certified Professional Practice Test

(ACS CP) American Chemical Society (ACS) Certified Professional Practice Test

ACS CP Thermodynamics & Chemical Kinetics 3