Kinetics Flashcards
What does it mean to study reaction kinetics?
Focused on studying how fast a process is by measuring changes over time.
What is a slow reaction compared to a fast reaction?
Slow - small change in [ ] overtime
Fast - large change in [ ] overtime
Define reaction rate
The change in [ ] divided by the time interval which the change is observed
m = change in [ ] / t
Can be determined through method of initial rates
How do we mathematically describe reaction rate?
Instantaneous Reaction Rate =
-d[reactant]/dt = +d[product]/dt
Define mass balance
Change in concentration for each component related to its coefficients
What does stoichiometry and mass balance help determine?
The rate of formation and the rate of consumption
Define rate law
An expression for the instantaneous reaction rate in terms of instantaneous concentration of the species involved in a reaction.
Rate = k[A]m[B]n
Define a rate constant
A proportionality factor in the rate law relating reagent concentrations to reaction rate
k
-change with temp
- unique in reactions
- Have different units
What does the reaction order do?
Shows the exponential dependence on each regent on the rate of reaction
Ex: m and n
Overall order = sum of exponents
How do you find the rate law?
It is experimentally determined, NOT through stoichiometric derivatives
How do you perform the method of initial rates? What does this method do?
Compare initial concentrations to the observed reaction rate to find the orders of the reaction. This ONLY depends on the reactants.
What do you use integrated rate laws for?
To describe how the [ ]’s change overtime
Ex: rate = 1/1 d[A]/dt
In[A]t - ln[A]0 = - kt
What order is this integrated rate law?
First order
A -> B
[A]t/[A]0 = e -kt
What order is this?
This is first order.
Just a algebraic manipulation that is given on the formula sheet
ln[A]t = -kt + ln[A]0
How do you recognize/ plot this graphically?
Y = m x + b respectively
ln[A]t = y
-kt = m
ln[A]0 = b
X is y intercept
1/ [A]t = kt + 1/[A]0
What order of integrated rate law is this?
A second order
Given on formula sheet
A + A -> B
2A -> B
A +B -> C
In a reaction of 2A -> B, what formula should you use to determine the time it takes for [A] to reach a 0.32M if [A]0 = 1.6M?
1/[A]t - 1/[A] = kt
How do you draw/recognize second order reactions graphically?
1/ [A]t = kt + 1/[A]0
y = mx + b
1/ [A]t = y
kt = m
1/[A]0 = b
What is pseudo- first order conditions?
Increase the concentration of one of two components relative to to the other, so the concentration appears constant over the course of the reaction.
k’
Done in lab
[A]t = -kt + [A]0
What order is this integrated rate law?
Zero order
A + B -> C
How do you draw/recognize this graphically?
[A]t = -kt + [A]0
Y = m x + b
What is the formula for a 0th order half life?
t1/2 = [A]0 /2k
What is the formula for the First order half life?
t1/2 = ln2/k
What is the formula for the second order half life?
t1/2 = 1/k[A]0
How does t1/2 vary throughout the first, second, and third orders?
0th order - t1/2 gets shorter
1st order - t1/2 is constant
2nd order - t1/2 is longer
Define the overall reaction
The balanced chemical equation. Accounts for all input and output NOT the intermediates
Define reaction mechanism
The step by step process. Shows intermediates
Define intermediates
Species that are produced and consumed during the reaction. Appear in the mechanism but not in the overall reaction
Define catalyst
Are consumed and regenerated. Do not appear in overall reaction
Define an elementary reaction
Transition state occurs in a single step
Define molecularity
The number of reactant molecular entities
What does it mean to be unimolecular ?
1 reactant molecule
What does it mean to be bimolecular?
2 reactant molecules
What does it mean to be termolecular?
3 reactant molecules (rare)
What is a reaction coordinate diagrams?
Energy diagram describing the path one molecule of reactant follows as it reacts to become products.
Shows change in G 2x dagger (how fast)
and change in G naught (how far)
Where is the transition state located on the reaction coordinate diagram?
At the highest energy point when going from reactants to products. Top of change in G 2x dagger.
How do you tell which reaction is slower and which is faster based on a reaction coordinate diagram?
The larger the change in G 2x dagger is, the slower the reaction is
