Kinetics: Rates and Mechanisms of Chemical Reactions

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

half life

K increases

if temperature increases

A reaction ______ is a hypothesis about how a reaction occurs. This hypothesis is tested to see if it fits with the experimentally observed ___ law.

mechanism, rate.

K

rate constant

the rate law for an overall reaction is equal to the rate law for the _______-_______ step

rate determining

What is the value f the structural orientation factor (p) based on?

the structural complexity of the reacting species.

R

universal gas constant

Place the steps necessary to determine reaction order from an integrated rate law in the correct order, starting with the first step at the top of the list.

1 Rearrange each rate law into an equation for a straight line (y=mx+b) 2 Plot y vs. x for each integrated rate law. 3 The linear plot indicates the order of reaction.

The steps for studying kinetics are summarized in the illustration. Match each lettered step with the appropriate action required.

A - Determine slop of tangent at t0 for each plot. B- Compare initial rates when the concentration of one reactant changes and the other is held constant (and vice versa) C- Substitute initial rates, orders, and concentrations into the rate equation and solve for K.

Which of the following statements correctly describe a reaction mechanism? Select all that apply.

A reaction mechanism describes a series of single reaction steps that sum to the overall chemical equation. A reaction mechanism is a hypothesis

Ea

Activation energy

Which of the following conditions must be satisfied for a collision between reactants to be effective?

Appropriate molecular orientation. Enough energy to overcome Ea.

What is an elementary step?

Each step that makes up a reaction mechanism.

Which of the following statements correctly describe the key aspects of drawing a reaction energy diagram.

For an exothermic reaction the energy of the products is less than the energy of the reactants. Intermediates will be higher in energy than any reactants or products.

a decrease in temperature leads to

a decrease in rate

T

absolute temperature

transition theory focuses on the formation of the ______ complex, which exists at the moment of highest ______ energy in a reaction

activated, potential

The _____ energy of a reaction is the energy threshold that colliding molecules must exceed in order to react.

activation

a decrease in Ea leads to

an increase in rate

a ______ is a substance that increases the rate of a reaction without being consumed. This type of substance is often used up and regenerated during the reaction.

catalyst

each reaction has its own characteristic reaction rate, which is determined by the nature of the reacting species. However, reaction rate can be influenced by increasing the frequency and energy of the ______ between molecules.

collisions

During the course of a reaction, reactant concentrations _____ and product concentrations _____.

decrease, increase.

A reaction energy diagram plots potential _____ versus reaction ____.

energy, progress

Delta H > 0

for an endothermic reaction

Delta H < 0

for an exothermic reaction

reaction orders are typically positive integers or zero but they can also be ______ or ______

fractional or negative

A

frequency factor

raising the temperature of a reaction increases the reaction rate by increasing the ______ and ______ of the collisions

frequency, energy

A catalyst that is in a different phase than the reactants is a(n) ______ catalyst.

heterogeneous

Ea (forward) <Ea (reverse)

if DeltaH<0

Ea (forward) >Ea (reverse)

if DeltaH>0

K decreases

if Ea increases

For any mechanisms, only _______ involved up to and including the ____ step appear in the overall rate law.

reactants, slow