Chemistry chapter 17
activated complex
A temporary union of atoms that forms after reactants have begun reacting but before products have formed is known as a _________________
Activation energy
____________________________ is the minimum energy required to transform the reactants into an activated complex
it increases by a factor of four
A reaction order is zero in reactant A and is two in reactant B. What happens to the reaction rate when the concentrations of both reactants are doubled?
catalyst
A ______________ provides an alternative energy pathway or reaction mechanism in which the potential-energy barrier between reactants and products is lowered
catalyst
A _________________ is a substance that changes the rate of a chemical reaction without itself being permanently consumed
homogeneous reaction
A ______________________ is a reaction whose reactants and products exist in a single phase
enzyme
A catalyst that increases metabolic processes is known as a ____________________
homogeneous catalyst
A catalyst that is the same phase as all the reactants and products in a reaction system is called a _______________________
rate ratio
A reaction order is found by comparing the concentration ratio with the ____________________
activated complex
A transitional structure that results from an effective collision and that persists while old bonds are breaking and new bonds are forming is called an _______________________
initial input
An __________________________ of energy is needed to overcome the repulsion forces that occur between reactant molecules when they are brought very close together
form products
An activated complex can best be as a unstable arrangement of colliding particles that can rearrange to _________________
rate law
An equation that relates reaction rate and concentrations of reactants is called _______________________ for the reaction
increase
An increase in surface are with __________________ the rate of heterogeneous reactions
increase
An increase in temperature will __________________ the average kinetic energy of the particles in a substance; this can result in a greater number of effective collisions
2
An order of ____ means that the reaction rate is directly proportional to the square of the reactant
0
An order of _____ means that the rate does not depend on the concentration of the reactant, as long as some of the react is present
1
An order of ______ for a reactant means that the reaction rate is directly proportional to the concentration of that reactant
endothermic; exothermic
Bond breaking is an ________________ process, and bond forming is an ____________________
1. the collision is not energetic enough to supply the required energy 2. the colliding molecules are not oriented in a way that enables them to react with each other
Collision theory provides two reasons why a collision between reactant molecules may fail a new chemical species. What are the two reasons?
In order for a reaction to occur, the molecules or atoms must collide with sufficient energy to overcome the activation energy barrier. The collision also must occur in the correct orientation, in most cases at a particular end of a molecule or atom.
Explain why the energy and orientation of the collision of atoms and molecules is important in chemical reactions.
single step
For a reaction that occurs in a ______________________, the reaction rate of that step is proportional to the product of the reactant concentrations, each of which is raised to its stiochiometirc coefficient
metals
_________________ are often used as heterogeneous catalysts
forming an activated complex with lower energy
How do catalysts affect reaction rates?
The energy of the activated complex is greater than the energy of the reactants and greater than the energy of the products.
How does the energy of the activated complex compare with the energies of reactants and products?
The rate law is determined from the slowest step, called the rate-determining step because it has the slowest rate.
Identify the step used to determine the rate law if a chemical reaction proceeds in a sequence of steps.
slowest step (because it has the lowest rate)
If a chemical reaction proceeds in a sequence of steps, the rate law is determined from the ________________
three
If the concentration of a reactant in a mixture is doubled and the reaction rate increases by a factor of reaction order with respect to that reactant is _____________
two
If the concentration of a reactant in a mixture is tripled and the reaction rate increases by a factor of nine, the reaction order with respect to that reactant is ________
increases
If the temperature increases, k ______________
homogeneous
In __________________reaction systems, reaction rates depend on the concentration of the reactants
their particles must collide
In order for reactions to occur between substances, what must happen?
transition state
In the brief interval of bond breakage and bond formation, the collision complex is in a _________________
experiments
________________________ are used to determine the probable sequence of steps in a reaction mechanism
activation energy barrier
Molecules must collide with enough energy to overcome the ___________
high
Only ions or molecules with very ____________ kinetic energy can over come repulsive forces and get close enough to react
1. with a favorable orientation 2. with enough energy to merge the valence electrons and disrupt the bonds of the molecules to form to the products
Reactant molecule must collide with what two things?
intermediates
Species that appear in some steps but not in the net equation are known as ___________________
T
T/F Chemical equations describe reactions, but do not show the reaction mechanism
T
T/F If the number of effective collisions increases, the reaction rate will increase
T
T/F The orders in the rate law may or may not match the coeffincients in the balanced equations
F
T/F The value of k does change for different concentrations of reactants or products
rate law
The ___________________ is applicable for a specific reaction at a given set of conditions and must be determined from experimental data
specific rate constant
The ____________________ is the proportionality of constant relating the rate of reaction to the concentrations of reactants
kinetic-molecular theory
The ______________________ states that the speeds, and therefore the kinetic energies, of the molecules increase as the temperature increases
reaction mechanism
The ________________________ is the step-by-step sequence of reactions by which the overall chemical change occurs
catalysis
The action of a catalyst is called ___________________
experimentally
The actual effect of concentration changes on reaction rate must determined ____________________
chemical kinetics
The are of chemistry that is concerned with reaction rates and reaction mechanisms is called __________________
reaction rate
The change in concentration of reactants per unit time as a reaction proceeds is called the ___________________
heterogeneous catalyst
When its phase is different from that of the reactants, it is called a _________________________
products and reactants
The energy change, delta E, for a reaction is the energy difference between the ___________________
reaction mechanism
The form of the rate law depends on the ____________________
activation energy
The minimum energy that two colliding molecules need chemical transformation can take place is the
order
The power to which a reactant concentration is raised is called the ____________ in that reactant
heterogeneous reactions
____________________________ involve reactants in two different phases
exothermic
The reaction for the formation of water from the diatomic gases oxygen and hydrogen is ________________
collision theory
The set of assumptions regarding collisions and reactions is known as ___________________
rate-determining step
The slowest rate step is called the ____________________ for the chemical reaction
1. the energy pathway that a reaction follows 2. the changes that take place on the molecular level when substances interact
The speed of a chemical reaction depends on what two things?
order of the reaction (overall order)
The sum of all the reactant orders is called the _______________________
n
The value of ____ is said to be the order of the reaction with respect to [A], so the reaction is said to be "nth order in A"
positive
The value of delta E for an endothermic reaction is always ____________
increases; remains unchanged
The value of k usually ______________ as temperature increases, but the relationship between reaction rate and concentration almost always ___________________
concentration ratio
To find a reaction order, compare the rate ratio with the _________________
kinetic energy
Two molecules cannot react if there is not enough _______________
1. nature of the reactants 2. surface area 3. temperature 4. concentration 5. presence of a catalyst
What are the factors that influence the rate of a chemical reaction?
the entire stepwise set of chemical reactions, including the intermediates along the pathway
What does a reaction mechanism show?
it provides more molecules that have the necessary activation energy and causes an increase in the reaction rate
What does raising the temperature of a reaction do?
the collision frequency of the reactants and on the collision efficiency
What does the rate of reaction depend on?
increases the reaction rate
What effect does adding a catalyst have on the reaction rate?
doesn't affect the reaction rate
What effect does changing concentration of a zero-order reactant have on the reaction rate?
decreases the reaction rate
What effect does decreasing reactant concentration have on the reaction rate?
decreases the reaction rate
What effect does decreasing surface area have on the reaction rate?
increases the reaction rate
What effect does increasing temperature have on the reaction rate?
a substance that oxidizes in air oxidizes more vigouously in pure oxygen
What is an example of the reaction rate depending not only on the surface area but also on the concentration of the reacting species in a heterogeneous reaction system?
Homogeneous reactions involve reactants and products that exist in a single phase. Heterogeneous reactions involve reactants in two different phases.
What is the difference between homogeneous reactions and heterogeneous reactions?
R = k[A]^n[B]^m
What is the general rate law form?
