AP CHEM: Unit 3 Kinetics (sec 2)

What is kinetics?

The study of the speed or rate of a reaction under various conditions.

Do thermodynamically favorable reactions mean fast reactions?

No, favorable reactions do not necessarily occur quickly.

What can affect the rate of a reaction?

Factors include the nature of the reactants, concentration, temperature, surface area, and catalysts.

How does concentration affect reaction rates?

More molecules present lead to more collisions, resulting in faster reactions.

Why do physical states of reactants matter?

Reactants in different physical states can collide more readily, affecting the reaction rate.

How does temperature influence reaction rates?

Increased temperature gives molecules more kinetic energy, increasing collision frequency.

What is the effect of surface area on reaction rates?

Greater surface area increases the chance of collisions, leading to faster reactions.

What is a catalyst?

A substance that speeds up a reaction without being consumed in the process.

What role do enzymes play in reactions?

Enzymes act as biological catalysts, sensitive to temperature and shape determined by intermolecular forces.

What is the collision theory?

It states that only a certain percentage of collisions between reactant particles result in a chemical change.

What is the orientation factor in collision theory?

Molecules must be oriented correctly during collisions for a reaction to occur.

What is activation energy (Ea)?

The minimum amount of energy required to initiate a reaction.

What is an activated complex?

An unstable intermediate state before forming the products, also known as the transition state.

What does the rate of a reaction depend on?

It depends on the change in concentration of reactants or products over time.

How is the average rate calculated?

Average rate = Change in concentration / Time interval.

What happens to reaction rates as reactants are used up?

Rates usually slow down as the reactants are consumed.

What is the relationship between rates of appearance and disappearance in a 1:1 mole ratio reaction?

The rate of appearance of products equals the rate of disappearance of reactants.

What is the differential rate law?

It relates the reaction rate to the concentrations of the reactants, not products.

What does the rate law expression look like?

Rate = k [A]^m[B]^n, where k is the rate constant and m, n are the orders of the reaction.

How is the overall reaction order determined?

It is the sum of the orders of each reactant in the rate law, based on experimental data.

What is the significance of the exponent in the rate law?

A greater exponent indicates that changes in the concentration of that reactant have a larger effect on the rate.

What is an Initial Concentrations Table?

A table used to determine reaction orders by varying initial concentrations and measuring initial rates.

How does changing the concentration of a reactant affect the rate?

The effect of concentration change on the rate is examined through experimental data.

What is the relationship between reaction rates and stoichiometry?

In reactions with non-1:1 mole ratios, the rate must account for the coefficients in the balanced equation.

What is the rate of disappearance of N2O5 if its rate is 4.2 x 10^-7 M/s?

The rate of appearance of NO2 and O2 can be calculated based on the stoichiometry of the reaction.

What happens to the rate constant (k) with temperature changes?

The rate constant changes with temperature and the presence of a catalyst.

What does it mean if a reaction is first order with respect to a reactant?

It means that the rate is directly proportional to the concentration of that reactant.

What is held constant to examine the data for other reactants?

The concentration of one reactant.

If the concentration of NH4+ is constant, what can be inferred about the rate?

The rate depends on the concentration of NO2-.

What is the rate law for a reaction that is first order with respect to NO2-?

RATE = k [NH4+]^m [NO2-]^n, where n = 1.

How do you determine the rate constant (k) using experimental data?

By using the rate law and plugging in known concentrations and rates.

What is the overall order of a reaction if it is first order in NH4+ and second order overall?

The reaction is first order with respect to NH4+ and second order overall.

What happens to the rate if the concentration of a zero-order reactant changes?

There is no effect on the rate.

What is the relationship between concentration and rate for a first-order reaction?

Doubling the concentration doubles the rate.

What is the relationship between concentration and rate for a second-order reaction?

Doubling the concentration quadruples the rate.

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

[A]t = -kt + [A]0.

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

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

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

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

How can you determine the order of a reaction using experimental data?

By analyzing how changes in concentration affect the rate.

What is the unit of the rate constant (k) for a second-order reaction?

M^-1·s^-1.

What is the unit of the rate constant (k) for a first-order reaction?

s^-1.

What is the unit of the rate constant (k) for a zero-order reaction?

M/s.

What does a straight line on a concentration vs. time graph indicate for a zero-order reaction?

It indicates a constant rate of reaction.

What does a straight line on a natural log concentration vs. time graph indicate for a first-order reaction?

It indicates a first-order reaction.

What does a straight line on a 1/concentration vs. time graph indicate for a second-order reaction?

It indicates a second-order reaction.

What is the effect of temperature on the rate of a chemical reaction?

Generally, increasing temperature increases the reaction rate.

What is the significance of the rate constant (k) in a reaction?

It indicates the speed of the reaction at a given temperature.

What is the overall order of a reaction if it is second order with respect to A and first order with respect to B?

The overall order is third order.

How can you use algebra to analyze reaction rates when concentrations are not constant?

By plugging in known values from different experiments to find relationships.

What is the initial rate of a reaction?

The rate of reaction measured at the very beginning when concentrations are known.

What does the term 'rate law' refer to?

An equation that relates the rate of a reaction to the concentration of reactants.

What is the effect of doubling the concentration of a first-order reactant on the rate?

The rate will also double.

What is the effect of tripling the concentration of a second-order reactant on the rate?

The rate will increase by a factor of nine.

What is the purpose of using graphical analysis in determining reaction orders?

To visually identify the relationship between concentration and time.

What is the equation used to calculate concentration changes over time?

ln[At] = -kt + ln[A0]

What is the half-life of a reactant?

The time required for the concentration of a reactant to reach half of its initial value.

How is the rate constant (k) calculated for a first-order reaction?

k = 0.693 / t½

What does a first-order reaction imply about the concentration of reactants over time?

The concentration decreases by half in regularly spaced intervals.

What is the molecularity of a unimolecular reaction?

A reaction involving a single molecule collision.

What is the molecularity of a bimolecular reaction?

A reaction involving two reactant molecules colliding.

What is the molecularity of a termolecular reaction?

A reaction involving three reactant molecules colliding at the same time.

What is an intermediate in a multi-step reaction?

A substance that is created and then consumed in a multi-step reaction.

What is the rate-determining step in a reaction mechanism?

The slowest step of a reaction that determines the overall rate.

What is the Arrhenius equation?

k = Ae^(-Ea/RT), relating rate constant to temperature and activation energy.

What is the effect of a catalyst on a reaction?

It changes the speed of a reaction without undergoing a permanent change.

What is a homogeneous catalyst?

A catalyst that exists in the same phase as the reacting molecules.

What is a heterogeneous catalyst?

A catalyst that exists in a different phase from the reacting molecules.

What does the slope of the ln k vs. 1/T plot represent?

The slope is equal to -Ea/R, where Ea is the activation energy.

What is the concentration of (CH3)3CBr after two minutes if the rate constant is 9.9 x 10-3 s-1?

Use the first-order reaction formula to calculate the concentration.

What is the relationship between temperature and the rate constant (k)?

k increases with increasing temperature.

What is the significance of the rate expression in a reaction?

It cannot be predicted from overall stoichiometry but can be determined from elementary steps.

What happens to the rate law when the slow step is not the first step?

More complex calculations are required to determine the overall rate law.

What is the role of enzymes in biological reactions?

Enzymes act as biological catalysts that speed up reactions at their active sites.

What is the definition of a reaction mechanism?

A sequence of bond-making and bond-breaking steps that occurs in a reaction.

How do catalysts affect the activation energy of a reaction?

They lower the activation energy but do not change the overall energy change (ΔE) of the reaction.

What is the purpose of plotting ln k vs. 1/T?

To determine the activation energy (Ea) of a reaction.

What is the concentration of a reactant after 20 minutes if the initial concentration is 2.0 M?

Calculate using the first-order kinetics formula.

What is the formula for calculating the time required for a reaction to be 75% complete?

Use the half-life and rate constant to determine the time.

What does the term 'elementary step' refer to?

Reactions that occur in a single step.

What is the significance of the overall stoichiometry in a reaction?

It must agree with the experimentally determined rate law.