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Level 137

Reaction Kinetics


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chemical kinetics
study of how fast chemical reactions occur
reaction rate
speed at which chemical reactions occur
catalyst
a substance that increase reaction rate w/o being permanently used up or changed. it lowers the activation energy needed for the reaction so more molecules have the necessary energy for a reaction
inhibitors
slow down reaction rates
average rate
change in concentration/change in time
collision theory
for a set of reactions to occur, molecules must collide
activation energy
Energy Diagram's hill bisector line
exothermic
A chemical reaction that releases energy
nature of reactants
rates are influenced by
surface area
an increase in this increases the rate of a heterogeneous reaction
Temperature
? T :: ? collisions :: ? rate of reaction
concentration
a mixture that has a large amount of solute in the solvent; a strong solution
presence of a catalyst
changes the rate of a reaction without being consumed
homogeneous catalyst
a catalyst that is in the same phase as all the reactants and products
heterogeneous catalyst
a catalyst that is in a different phase
enzymes
biological catalyst
rate law
an equation that relates reaction rate and concentration at a certain temperature
reaction order
the power to which the reaction is raised is the order
reaction order 0
- rate doesn't depend on reactant
reaction order 1
rate is directly proportional to that concentration
reaction order 2
rate is directly proportional to the square
Reaction Kinetics
The study of the rates of reactions and the factors which affect the rates
Measuring Change in Colour
Measure absorption of absorbed chemicals & colour intensity using a spectrophotometer
Measuring Change in Temperature
Insulate reaction, measure with a thermometer
Gas Production
Gas collection apparatus measures volume of new gas
Change in pH
If there is an acid involved which is consumed & neutralized, the change is measured with a pH meter
Requirements for a Successful Collision
Colliding particles need enough KE so reactant bonds can be broken, Favourable collision geometry (the hug)
Factors Affecting Reaction Rates
Concentration, temp (move faster & more KE), surface area & phase, nature of reactants (strength of bonds), presence of a catalyst (new pathway)
Enthalpy
Amount of energy within a system
Activated complex
a transitional structure that results from and effective collision that persists while old bonds are breaking and new bonds are forming.
Kinetic Energy
energy of motion
Potential Energy
stored energy due to position or height
Inhibitor
Like a catalyst but slows down a reaction
Elementary Process
Individual step
Reaction Mechanism
a SEQUENCE of single reaction steps that sum to the overall equation
Reaction Intermediate
a substance formed and used up throughout the steps of a reaction mechanism
rate determining step
In a multi-step reaction, the slowest step is _
combustion
This is the reaction of a fuel with oxygen producing an oxide. This is an oxidation reaction.
corrosion
Example of a slow chemical reaction
decreases increases
during a chemical reaction, reactants transform into products. The quantity of reactants _______ over time and the quantity of the products _______ over time.
elementary step
is the step where one bond breaks or one bond forms
intermediate
is a species that is a product in an early step of the mechanism and a reactant in a later step of the mechanism.
Rate Determining Step (RDS)
RDS is the slowest step in the reaction mechanism. It governs the rate of the overall reaction and is the step of the reaction that has the MOST Ea (Activation Energy)
the atoms, molecules, or ions MUST collide in the correct orientation.
what two things have to occur to lead to an effective chemical change?
transition state
In each individual step of a reaction, the state of highest energy between reactants and products. The transition state is a relative maximum (high point) on the reaction-energy diagram.
positive (Ea = +)
Exothermic - Ea is always _______
Reactant Concentration
the higher the concentration of reactants the faster the the reaction rate.
What is a Catalyst ?
it is a substance that speeds up a reaction without itself being consumed during the reaction. (meaning throughout the reaction it remains unchnaged)
Addition of a catalyst
the addition of a catalyst speeds up the reaction by lowering the activation energy needed for effective collisions.
Quicker reactions
raise temperature
Lower temperature
Slow a reaction
less
When a light ray is totally internally reflected, does the second medium have to be more or less optically dense than the original?
more
The _______ the change in speed, the more the light beam changes direction.
Rate=?[A]^m[B]^n[C]^p....
general form of any rate law
K =
rate constant
reactants
A starting material in a chemical reaction
m,n,p... =
the order of each reactant
order of a reactant
gives an indication of how important the concentration of that reactant is to the overall reaction rate.It can only be determined by an experiment.
Method of Initial Rates
how you figure the order of each reactant.
1
if the concentration doubles and the rate doubles the order of that reactant is:
1
if the concentration triples and the rate triples the order of that reactant is:
2
if the concentration doubles and the rate quadruples the order of that reactant is:
0
if the concentration changes in any way and the rate remains constant the order of that reactant is: