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
