Chapter 13: Chemical Kinetics Flashcards
What is chemical kinetics?
It is the study of how fast reactions happen and the rate of chance of the reactions.
What do catalytic converters do? What does this require?
They accelerate the rates of chemical reactions that turn NO and other pollutants into nonpolluting products. This requires an understanding of chemical kinetics.
What does the rate of a reaction depend on?
- The physical state of the reactant
- The concentration of the reactants
- The temperature
- A catalyst
How does the physical state of the reaction affect the rate?
Kinetic energy increases from solid to gas
Solid: slow b/c not much KE,
How does the concentration affect the rate of the reaction?
It depends on the order of the reaction with respect to each reactant.
How is the order of the reaction discovered?
Experimentally not mathematically.
What is the relative rate? How is it written?
It is how reactants and products change with respect to each other and to time
“How do these reactions relate”
A[X]/At
All parts equal each other. Reactants are negative, products are positive. Coefficients are noted as a denominator.
What are the units of a reaction rate?
Molarity/seconds
What is a first order reaction?
A rate that depends linearly on only one reactant concentration (ie double concentration double rate)
What is a second order reaction?
Reaction proceeds at a rate proportional to the square of the concentration of one reactant (ie if you double the concentration the rate quadruples)
What is a third order reaction?
The minimum number of molecules necessary for the reaction to take place is three
What is a zero order reaction?
A reaction where the rate does not vary with an increase or a decrease in the concentration of the reactants.
How do you use experimental results to determine the order of the reaction with respect to a certain reactant?
Select two experiments in which the concentration of the reactant in question changes while the other reactant remains the same.
What are the units for a zero order reaction?
M/s
What are the units for a first order reaction?
1/s
What are the units for a second order reaction?
1/Ms
What are the units for a third order reaction?
1/M^2 s
What is the use of integrated rate laws?
To determine the reaction rate at anytime using only one experiment. (Calculus is used to create integrated rate law)
What is the rate law, integrated rate law, and half-life expression of a zero order reaction?
What is the y vs x and slope of the integrated rate law?
Rate = k
[X] = -kt + [X]0
t1/2 = [X]0/2k
[X] vs t m= -k
What is the rate law, integrated rate law, and half-life expression of a first order reaction?
What is the y vs x and slope of the integrated rate law?
Rate = k[X]
ln[X] = -kt + ln[X]0
t1/2 = 0.693/k
ln[X] vs t m=-k
What is the rate law, integrated rate law, and half-life expression of a second order reaction?
What is the y vs x and slope of the integrated rate law?
Rate = k[X]^2
1/[X] = kt + 1/[X]0
t1/2 = 1/k[X]0
1/[X] vs t m = k
What affects the rate constant k?
k is not affected by concentration
k is affected by temperature
Why does temperature affect the rate of a reaction?
Increased temperature increases Kinetic energy which increases the movement of the molecules and therefore the molecular collisions that break old bonds and build new bonds
What is activation energy?
Activation energy is the minimum energy of a molecular collision required to break reactants and build products.
What does the Arrhenius equation do?
It incorporated the factors of temperature and activation energy into the constant k.
What is the activation energy with respect to a reaction coordination diagram?
Activation energy = highest point on the diagram - the initial energy of the reactants.
What is the relationship between temperature and rate?
This relationship is not linear. It is exponential: k = Ae ^ -Ea/RT
What is A in the Arrhenius equation?
A is the collisions frequency factor, that is, the number of successful collisions. Reactants must be in the correct orientation to react.
What is R and T in the Arrhenius equation?
R is the gas law constant and T is temperature in Kelvin
What makes the relationship between temperature and rate linear?
ln k = -Ea/R (1/T) + ln A
What happens in the reaction when an increase in temperature increases the rate of the reaction?
The fraction of collisions with total kinetic energy greater than Ea increases.
What is a transition state?
It is a species (or state) corresponding to an energy maximum on a reaction energy diagram
How do we determine with elementary step is the slowest?
Write the rate law of each step and the slowest will match the overall rate law.
What are the aspects of a coordinate diagram?
Activation energy: highest point - initial energy of the system (reactants)
Activated complex (high energy transition state): highest point: old bonds breaking new bonds form
What is the point of reaction mechanisms?
Reaction mechanisms tell exactly what is happening in the reaction, that is, what molecules are colliding in what orientation. They can be used to determine a rate of reaction and the rate law, but this must match experimentally determined
What is the relationship between the activation energy and the constant.
Low activation energy means a large constant meaning a fast reaction.
Can the Arrhenius equation be used to determine a temperature?
Yes, if you have a final and initial constant and an initial temperature you can determine a final temperature
What is a reaction mechanism?
It is a set of steps at a molecular level (it is broken into elementary steps). Could be bimolecular (two molecules as reactants) or unimolecular (one molecule as reactant)
What are intermediate molecules?
Molecules produced in one step and used up in another
What is the rate-determining step?
It is the slowest step that determines how fast a reaction will occur. This is important for organic chemistry
