Chemical Kinetics and Reaction Mechanisms

Flashcards covering reaction kinetics, determining rate equations, reaction mechanisms, reaction order, and pseudo-order reactions based on the lecture notes.

What equation is used to calculate the change in reaction rate when reactant concentrations are varied?

$$\text{rate factor} = \text{concentration factor}^{\text{power}}$$

If doubling the concentration of reactant $A$ in a reaction makes it $8$ times faster, what is the exponent $p_A$ for reactant $A$?

$p_A = 3$, because $2^{p_A} = 8$.

What was the calculated rate constant $k$ using the set 3 data from the lecture's example problem?

$$k = 0.045$$

Why do chemists treat the rate constant $k$ as a pure number without quoted units?

Because the actual units of $k$ depend on the specific exponents in the rate equation and change for every reaction process.

Who determined one of the earliest reaction mechanisms for $H_2 + I_2 \rightarrow 2HI$?

Polanyi, a Nobel Prize winner from McGill University in Canada.

What are the three possible mechanisms for the reaction $H_2 + I_2 \rightarrow 2HI$ discussed in the lecture?

Mechanism 1: The $H-H$ bond breaks first; Mechanism 2: The $I-I$ bond breaks first; Mechanism 3: The $H-H$ and $I-I$ bonds break simultaneously.

Which mechanism was experimentally confirmed by Polanyi for the reaction $H_2 + I_2 \rightarrow 2HI$?

Mechanism 3, where the $H-H$ and $I-I$ bonds break simultaneously in the slow step.

How is reaction order defined in chemical kinetics?

Reaction order is defined as the sum of the exponents in a rate equation.

What is the overall reaction order for the one-step reaction $3A + 4B \rightarrow P$?

Seventh order (reaction order = $7$), because the sum of exponents is $3 + 4 = 7$.

What does reaction order conceptually measure regarding a chemical reaction?

It is a statistical description measuring how many molecules or events must successfully meet simultaneously to bring about a reaction.

What is the true theoretical reaction order for the one-step reaction $Ca + 2H_2O \rightarrow Ca(OH)_2 + H_2$?

Third order, corresponding to the rate equation $\text{rate} = k [Ca]^1 [H_2O]^2$.

What is a pseudo order reaction?

A reaction that acts like a lower order reaction than it actually is because one of the starting materials is a solvent and therefore has a constant concentration.

What true one-step first-order reaction was cited as an example in the lecture?

$$N_2O_8 \rightarrow 2NO_4$$