Unit 4 - Chemical Kinetics Flashcards
The study of the rates of chemical reactions.
Chemical kinetics
Change in concentration of a reactant or product per unit time.
Reaction rate
Factors that affect reaction rate.
Concentration
Activation energy
Nature of reactants
Temperature
Presence of catalyst
Molecular collisions
It explains why the other factors affect the rate of reaction.
Collision theory
Which of the following states that for the reaction to occur atoms or molecules or ions in a reaction system must do?
A. Collide.
B. Collide with enough energy to break and form bonds.
C. Collide with the proper orientation for a reaction to occur.
D. All of the above.
D
A collision that results in a reaction.
Effective collision
T/F
Reaction rate is proportional to effective collisions.
T
Also known as activated-complex theory.
Transition state theory
Transition state theory postulates that reactants form a high energy intermediate, the _____, which then falls apart into the products.
Transition state
T/F
For a reaction to occur, the reactants must acquire sufficient energy to form the transition state.
T
This energy is called the _____.
Activation energy or Ea
Minimum amount of energy required to initiate a chemical reaction.
Activation energy (Ea)
T/F
For any reactant, the bond type, strength, and number determine the Ea required for a successful collision.
T
Increased reaction rate is observed when reactants have _____ bonds.
Fewer and weaker
Reactions between MOLECULES are usually _____ than reactions between IONS.
Slower
T/F
Some reactions involve complicated molecular substances or complex ions are often more reactive than smaller, less complex entities.
F
Increase in concentration of _____ increases the likelihood for reactant molecules to collide (increase the reaction rate).
Reactants
Reducing volume or increasing pressure on a gas will cause a concentration to _____.
Increase
Increasing the surface area of a solid _____ the concentration of available particles.
Increases
T/F
The average rate decreases as the reaction proceeds. This is because as the reaction goes forward, there are fewer collisions between reactant molecules.
T
T/F
The average rate of reaction over each interval is the change in concentration over change in time.
T
A constant of proportionality between the reaction rate and the concentration of reactant.
Rate constant (k)
T/F
Rate is directly proportional to the concentration of the reactant.
T
T/F
Each reaction has its own equation that gives its rate as a function of reactant concentrations.
T
Expresses how the rate depends on concentration.
Differential rate law (rate law)
T/F
Rate law is the expression that gives the rate as a function of concentration.
T
T/F
Rate law expresses the relationship of the rate of a reaction to the rate constant and the concentrations of the reactants raised in some powers.
T
If aA → products, then the rate law is?
rate = k[A]^x
T/F
Reaction order (x) is determined experimentally.
T
It specifies the relationship between concentration of reactant and the reaction rate.
Reaction order (x)
T/F
Reaction order is not related to stoichiometric coefficient of the reactant in the balanced equation.
T
Reaction order is always defined in terms of _____.
Reactant concentrations
What is the reaction order when [A] increase 2x and rate is NOT affected.
Zero order
What is the reaction order when [A] increase 2x and rate increase 2x.
First order
What is the reaction order when [A] increase 2x and rate increase 4x.
Second order
If aA + bB→ products, then the rate law expression is?
rate = k[A]^x[B]^y
It is defined as the sum of the exponents on the reactants in the rate law.
Overall order of reaction (x+y)
Overall balanced chemical equation does not tell how a reaction actually takes place, but a _____ does.
Reaction mechanism
Sequence of elementary steps that leads to product formation.
Reaction mechanism
A sum of elementary steps or elementary reactions.
Reaction mechanism
A series of simple reactions that represent the progress of the overall reaction.
Reaction mechanism
It is one step in a series of simple reactions that show the progress of a reaction at the molecular level.
Elementary step
Refers to the number of molecules reacting in an elementary step.
Molecularity of a reaction
It appears in the reaction mechanism but not in the overall balance equation.
Intermediate
The first elementary step is the _____.
Rate-determining step
The slowest steps in sequence of steps leading to product formation.
Rate-determining step
T/F
The rate-determining step will give you the rate law expression.
T
Which of the following is/are true when temperature increases?
A.. Molecules move faster.
B. High kinetic energy.
C. More molecular collisions.
D. Higher reaction rates.
E. All of the above
E
T/F
At higher temperatures, the fraction of molecules with energy equal to or greater than the Ea also increases.
T
A substance that increases the rate of a chemical reaction without itself being consumed.
Catalyst
Catalyst may react to form an _____, but it is regenerated in the subsequent step of the reaction.
Intermediate
Catalyst increases the rate by _____ of the reaction.
Lowering the activation energy
Reactants and catalyst are in different phases.
Heterogenous catalyst
Examples of heterogeneous catalyst.
Haber synthesis of ammonia
Ostwald process of HNO3
Catalytic converters
Reactants and catalyst are in dispered in a single phase.
Homogeneous catalyst
Examples of homogeneous catalyst.
Lead chamber process – for the production of H2SO4
Acid-base catalysts
It involves enzymes (biological catalysts) that have active site that specifically bind to substrates (reactants).
Enzyme catalysis
