KINETICS Flashcards
What are rate laws used for?
Rate laws are used to relate the rate of a chemical rxn to concentrations of the reactant
What are rate laws dependant on?
Mechanisms (what breaks first, what bond forms first, any intermediate chemical species, etc…)
What is the kinetics definition of equilibrium?
Equilibrium is established when when both the forward and reverse rxns are occuring at the same rate (dG = 0)
What are reaction rates?
Reaction rates are a measure of the change of a chemical species as a function of time
What is the reaction rate formula?
What are the units for rate?
M/s
What are the factors which affect rate?
- Medium (surface area)
- Concentration
- Temperature
- Catalysis
What does more surface area do to the rate of a reaction?
Increases the rate of rxn
How does the reaction react when more material is readiily available?
It occurs faster
What happens to the rate of reaction when temperature is increased?
The higher the temperature the more molecules with sufficient energy to get over the energy barrier. Thus all elementary rxns have a faster rate at higher temperatures
How does a catalyst change the rate of a reaction?
A catalyst essentially changes the rxn mechanism for a rxn, allowing it to proceed at a faster rate by lowering the energy barrier between the reactants and products (activation energy)
What is the rate for zeroth order?
Rate = K
What is the integrated rate law for zeroth order?
[A] = [A]° - kt
What is the slope for zeroth order?
Negative
What is the half-life for zeroth order?
t1/2 = [A]° / 2K
What is the unit for zeroth order?
M/s
What is the rate for first order?
Rate = K[A]
What is the integrated rate law for first order?
ln[A] = ln[A]° - Kt
What is the slope for first order?
Negative
What is the half-life for first order?
t1/2 = ln2 / K
What is the unit for first order?
1/s
What is the rate for second order?
Rate = k[A]^2
What is the integrated rate law for second order?
1/[A] = 1/[A]° + kt
What is the slope for second order?
Positive
What is the half-life for second order?
t1/2 = 1 / K[A]°
What is the unit for second order?
1/Ms
What is pseudo-first order?
Pseudo-first order is when the concentration of a reactant remains constant ( [A] >>>>> [B] ) to where the rate law goes from K[A][B] to k’[B]
Why do we integrate rate laws?
To yield an equation of the concentration of a particular species as a function of time
What is a zeroth order reaction?
A zeroth order reaction is when the rate of rxn is independent of all the concentrations of the reactant, meaning that the rate of the rxn will not change as the rxn proceeds and is therefore constant with time
What is a first order reaction?
A first order reaction is when a rxn is overall first order in respect to one of the reactants, then the rate of the rxn is simply proportional to the amount of that reactant
What is a second order reaction?
A second order reaction is the result of bimolacular steps occuring iin a rxn; involves a collision between 2 different cmolecules, which results in the rxn being second order overall, but one that is first order with resppect to two rxns
What is a reaction mechanism?
A reaction mechanism are the steps in a chemical rxn or rather a breakdown of what actually happens during the course of the rxn
How many reactants are involved in a unimolecular reaction?
1
How many reactants are involved in a bimolecular reaction?
2
What is the rate limiting step?
The rate limiting step is the slowest step, which can be used to approximate the rate of the overall rxn when a rxn involves many steps
What is the basis for Arrhenus Law?
All chemical rxns may increase in rate as the temperature is increased
How do you speed up the rate of a rxn based on Arrhenius Theory?
- Increase the temperature
- Lower the barrier
What is a reaction coordinate?
A reaction coordinate is the path that links the reactant molecules to the product molecules
What do the minima indicate?
intermediates
What do the peaks indicate?
Transition states
What is a trasition state?
A transition state is the high energy point between 2 minima along the rxn coordinate; in the middle of the breaking of the old bond and the forming of the new bond
What is the activation energy?
The activation energy is the height of the barrier along the rxn pathway
What is the formula for Arrhenieus Law?
Which barrier is the rate limiting step?
The largest barrier
How do catalysts work?
Catalysts provide a mean for the reactant molecules to break bonds and then form temporary bonds with the catalyst
What determines the order of each species in an empirical rate law?
The exponent
Rate = k[A]x[B]y
How do you determine the order of a species on a given table?
When comparing 2 lines…
K [line 2 / line] x [line 2/line1] y
The order you are looking for is the species which is undergoing a change
