S2 Fulton L1-4 Flashcards
(51 cards)
What is the RDS
The rate determining step, the slowest step in a multistep process
What is the rate law
The rate law is an algebraic equation which describes the dependence of the reaction rate upon the concentration of compounds involved
What is the rate constant
The rate constant is the proportionality constant on the rate law. It allows us to put a number on how fast or slow a process goes.
What are we measuring when we measure kinetics
When we measure kinetics we are measuring how concentrations of reactions and/or products change as a reaction proceeds
What does the study of reaction kinetics allows us to do
- determine rate law, these rate laws leads to an understanding of molecularity
- measure rate constants
Define molecularity
The number of molecules that come together to form an activated complex (unimolecular or bimolecular)
What does measuring rate constants allows us to do
This allows us to relate the changes in solvent, structure, catalyst to the rate of reaction
What is a kinetic profile
A kinetic profile describes how the concentrations of reactants and products change over time during a chemical reaction.
How can we obtain reaction kinetics
Measure changes in concentration of reagents and/or products by UV, FTIR, NMR spectroscopy (either continuously or by taking aliquots of reactions)
How would decreasing reagents starting concentration affect the reaction kinetics
Decreasing the starting concentration of reactants the slower the reaction will become
What do we use the kinetic data for
We use the kinetic data to test a rate law
How would we know the rate law is first order
If plot of rate vs concentration is linear, shows rate is first order in that reagent/products
How would we know the rate law is second order
If rate vs concentration is not linear, then plot rate vs concentration^2: a straight line shows rate is second order
Describe the difference between reaction order and molecularity
Reaction order is the exponent in an algebraic equation that relates rate of a reaction to concentration of reagents. It can be zero, integer or fractional. Molecularity is the number of species involved in an elementary process. It can only be 1 or 2.
How can we use integrated rate laws to interpret kinetic profiles
If plot of ln[A] vs t is linear then the reaction is first order. If plot of 1/[A] vs t is linear reaction is second order
What is an important thing to note when we talk about proposed reaction mechanisms
Note that rate laws cannot prove a reaction mechanism: they can support a proposed mechanism, and they can also be used to discount a proposed mechanism
What are labelling experiments
Labelling experiments allow us to correlate atoms in products with starting material, information which can provide mechanistic insight
What are the common labels for H 12C and 16O
D for H
13C for 12C
18O for 16O
Describes the labels for labelling experiments
All labels are non-radioactive. Easy to spot their incorporation by mass spectrometry, and 13C and D can be detected by NMR spectroscopy
What is a crossover experiment
A crossover experiment uses labelled and unlabelled versions of reactants mixed together to see if mixed (crossover) products form, which indicates intermolecular exchange or reaction.
What is a double labelling experiment
A double labelling experiment involves tagging two different atoms or positions in a molecule with labels to observe two variables at once.
What is a single labelling experiment
A single labelling experiment involves tagging one atom or molecular position with a detectable label to trace its movement, transformation, or role in a chemical system.
Why type of labelling experiments are generally the most useful
Double labelling experiment are more useful
What is the Hammett equation
Log kx/kH = pσx
