Chapter 14 - Chemical Kinetics and Reaction Rates

Flashcards covering topics from lectures on chemical kinetics, rate laws, reaction mechanisms, and the effect of temperature and catalysts on reaction rates.

What do M, R, and T stand for in gas-related equations?

Molarity (mol/L), Gas Constant (0.08206 L·atm/mol·K), Temperature (Kelvin)

What is the theoretical van't Hoff factor (i)?

The ratio of moles of solute particles to moles of formula units dissolved.

What is ion pairing?

Oppositely charged ions associating with each other in solution.

What is the van't Hoff factor (i) for nonelectrolytic solutes?

i = 1

What is chemical kinetics?

The study of the rates/speed of reactions.

What is the collision model?

A reaction takes place between particles when they collide.

What factors impact reaction rates?

Concentration of reactants, temperature, and structure & relative orientation of colliding particles.

How is the rate of a reaction measured?

Measured as the change in amount of a reactant or product over time.

How do you calculate the generalized reaction rate?

Use stoichiometric coefficients to normalize the individual changes in concentration.

What is the average rate of reaction?

The rate of reaction over a time interval.

What is the instantaneous rate of reaction?

The rate of the reaction at a specific instant in time.

What is a rate law?

Mathematical equation that expresses the relationship between the rate of a reaction and the concentration of reactants; determined experimentally.

What is the general form of a rate law for the reaction A + B -> products?

r = k[A]^m [B]^n

What does the reaction order reflect?

Reflects the rate's sensitivity to changing that reactant's concentration.

What does the rate constant (k) depend on?

Depends on the specific reaction and temperature; doubling k doubles the rate.

Describe a zero-order reaction.

Rate = k; units are M/s; rate is constant as reaction proceeds.

Describe a first-order reaction.

r = k[A]; units are 1/s; rate is directly proportional to reactant concentration.

Describe a second-order reaction.

r = k[A]^2; units are 1/(M·s); rate is directly proportional to the square of the reactant concentration.

How are rate laws and reaction orders determined experimentally?

Measure initial rates of reaction under a set of initial concentrations for the reactants.

What is a differential rate law?

Relates reactant concentration and instantaneous rate: r = k[A]^n

What is an integrated rate law?

Relates reactant concentration to reaction time, used for determining the amount of reactant present/remaining at a certain time.

What is the integrated rate law for a zero-order reaction?

[A] = -kt + [A]0

What is the integrated rate law for a first-order reaction?

ln[A] = -kt + ln[A]0

What is the integrated rate law for a second-order reaction?

1/[A] = kt + 1/[A]0

What is half-life?

The amount of time it takes for the initial concentration of a species to decrease by 50%; depends on reaction order.

What is the half-life equation for a zero-order reaction?

t1/2 = [A]0 / (2k)

What is the half-life equation for a first-order reaction?

t1/2 = ln(2) / k

What is the half-life equation for a second-order reaction?

t1/2 = 1 / (k[A]0)

What is the Arrhenius equation?

Mathematical relationship between the magnitude of the rate constant and other factors.

What is the Arrhenius equation?

k = Ae^(-Ea/RT)

What is activation energy (Ea)?

The minimum amount of energy needed for a reaction to take place.

What is the frequency factor (A)?

The # of times a reactant approaches an activation barrier per unit time.

What is the orientation factor (p)?

The fraction of collisions that have a proper orientation for a reaction to occur.

What is the linearized form of the Arrhenius equation?

Linearized form: ln(k) = (-Ea/R)(1/T) + ln(A)

What is the two-point form of the Arrhenius Equation?

in(k2/k1) = -Ea/R (1/T2 - 1/T1)

What are the requirements for an effective collision?

The collision between particles must have the necessary orientation and enough energy to overcome the activation barrier.

What are reaction mechanisms?

Simple steps that reactants go through to make final products.

What is an elementary reaction?

A single reaction step that cannot be broken into simpler steps.

What are the two requirements for a valid reaction mechanism?

When summed, the individual steps of the mechanism must add up to the overall balanced reaction and account for the experimentally determined rate law.

What is molecularity?

The # of reactant particles that enter into an elementary reaction.

What is a unimolecular reaction?

Elementary reaction that involves only 1 particle.

What is a bimolecular reaction?

Elementary reaction that involves 2 particles colliding.

What is a termolecular reaction?

Elementary reaction that involves 3 particles colliding (rare).

How does the rate-determining step affect the overall reaction rate?

The slowest step of the mechanism determines the rate of the entire mechanism.

How is the rate-determining step identified?

Step with the highest activation energy.

What is a catalyst?

Chemical species that increase the rate of the reaction but are not ultimately consumed.

How does a catalyst work?

Lowers the activation energy of the reaction by changing the mechanism.