rates of reaction Flashcards
chemical kinetics
the study of rates of chemical reactions and the factors that influence these rates
Synonymous with rates of reaction
HOW WILL WE MEASURE REACTION RATES?
The rate of appearance of product or the rate of disappearance of reactants
o Units are mol/L/s
Reaction rate
number of atoms, ions, or molecules that react in a given time to form products
COLLISION THEORY
atoms, ions, and molecules can react to form products when they collide with one another, provided that the colliding particles have enough kinetic energy
collision between reactant molecules must have the correct orientation in order for a chemical reaction to take place
activated complex
peak of the activation energy barrier is a very unstable formation of an arrangement of atoms
it is also called the transition state as it has equal chance to become products or return to original states
o lifetime is about 10^-13s
FACTORS THAT IMPACT CHEMICAL KINETICS
Concentration (for homogeneous reactions) or particle size (for heterogeneous reactions)
Temperature
Prescence of a catalyst
Nature of the reactants
inhibitor
A substance that interferes with catalysis
Instantaneous Rate
the reaction rate calculated at a single time during the course of a reaction (oh god derivatives)
Initial Rate
The reaction rate calculated at the beginning, prior to any substantial chemical reactions. No interference!
reaction mechanism
the step by step sequence of elementary reactions by which overall chemical change occurs (for complex reactions!!)
Elementary Step
each step in a reaction mechanism
reaction intermediates
Substances that are formed in one step of the reaction mechanism and used up in a later step
rate determining step
slowest step in a reaction, basically determines how fast the reaction goes
basically the one with the highest activation energy
activation energy
minimum energy that colliding particles must have in order to react
POTENTIAL ENERGY!!
explains why some exothermic reactions do not occur at room temperature
maxwell-Boltzman Distribution
The distribution of speeds/energies in a chemical reaction.
can use to show the threshold energy
threshold energy
The minimum energy that molecules must have in order to break bonds
KINETIC ENERGY!!
For typical reactions, the threshold energy is out in the tail section of the distribution curve
where should the threshold energy barrier move for a faster reaction or slower reaction?
move to the LEFT for a faster reaction
move to the RIGHT for a slower reaction
what kind of threshold energies would very fast reactions have?
LOWER ones
what kind of threshold energies would very slow reactions have?
HIGHER ones
10c temperature change impact on M-B distribution?
it can often double a reaction rate
Average KE (temperature) increases only slightly, the portion to the right of the threshold energy barrier doubles in size
catalyst impact on potential graph/reaction?
provides an alternative route for the reaction with a lower!!!! Activation energy!!
on a graph, it lowers the thingy for activation energy
It is important to remember that a catalyst doesn’t actually lower the activation energy
It provides an alternative reaction pathway
Homogenous catalysts
are in the same phase as the reactants
They work by providing a new mechanism in which they react in an early step and are recreated in a later step
No net loss of catalyst!!!
Heterogenous catalysts
are in a different phase than the reactants
Most of the time they be solids and the reactants flow over the surface
how do catalysts work
Reactant molecules are absorbed onto the catalyst surface
The molecules bonds are weakened as they stick to the surface
Also!! Molecules are held in a position so that when other molecules collide with them, chances are better off having an effective collision
Think of GOLF!! Teeing a ball up to get a better shot at it! Compared to trying to hit it out of the rough or a sand trap!
elementary reaction
reactions that only need one step!
Activated Complex/Transition State Theory
Rates of reaction can be studied by examining activated complexes!
The activated complexes can convert into products, and kinetic theory can be used to calculate the rate of this conversion.
(from wikipedia^^)
basically it wants to explain activated complexes and how reactions occur
ANYWAY JUST THINK OF maxwell-Boltzman Distribution AND THRESHOLD ENERGY
what is a specific rate constant (k) for a reaction?
number that relates concentration of a reaction to the rate of reaction
how do you determine the actual kinetic order of a reaction?
by the experiment! collect data!
effective collision
reaction where there IS a change!
ineffective collision
reaction where nothing happens, the products are the same as the reactants
