Quiz 2 - Chemical Kinetics: Mechanisms | Chemical Kinetics: Mechanisms

The activation energy E_a is the energy that must be provided to compounds to result in a chemical reaction.

Arrhenius equation:  ln K = - Ea/RT + ln A

ln k is proportional to 1/T ⇒ A plot of ln k as a function of 1/T is linear

ΔH_rxn = E_{a forward} – E_{a reverse} = 40 – 55 = - 15 kJ

The step which is much slower than any of the other steps controls the overall reaction rate
⇒ step (1) is the rate-determining step

Elementary reactions have reaction orders equal to the stoichiometric coefficients for each reactant 
⇒ rate law of (1) = k[NO₂][F₂]

Elementary reactions have reaction orders equal to the stoichiometric coefficients for each reactant
⇒ rate law of (1) = k₁ [NOCl];    rate law of (-1) = k_-1 [NO][Cl];    rate law of (2) = k [NOCl][Cl]

For reversible reactions, rate of forward reaction = rate of reverse reaction at equilibrium
⇒ k₁ [NOCl] = k_-1 [NO][Cl]

The step which is much slower than any of the other steps controls the overall reaction rate
⇒ step (2) is the rate-determining step

The rate law of this reaction is: k [NOCl][Cl] = $\frac{{\mathrm{k}}_{-1}}{{\mathrm{k}}_1}$ [NO][Cl]² = $\frac{{\mathrm{k}}_1}{{\mathrm{k}}_{-1}}$ [NOCl]²/[NO]

A catalyst lowers the activation energy barrier of the reaction by providing a new path for the reaction without being consumed in the reaction.

The pre-exponential factor A in the Arrhenius equation is related to the frequency of effective collisions and the orientation of molecules during collisions.

A unimolecular elementary reaction involves a single molecule undergoing dissociation or rearrangement to form products.

Increasing the concentration of reactants leads to more frequent collisions, increasing the likelihood of effective collisions that result in a reaction.

The rate-determining step is typically the slowest step, which is usually the one with the largest activation energy.