Chapter 14: Chemical Kinetics Flashcards
Four important factors which affect the rate of reaction
Reactant concentration
Temperature
Action of catalyst
Surface area
Reaction rate
Change in concentration (M) per unit time (s)
There are two ways of measuring rate
Speed at which products appear (change in miles of b per unit time)
Or
Speed at which reactants disappear (change in miles of a per unit time)
Average rate=
-change in moles of a/ change in time
Or positive b
Reaction rate is given by
-1/a (change in concentration of a/ change in time) = 1/b (change in concentration of b/ change in time)
Rate laws
Show if and how the rate of a reaction depends on the initial concentration of the reactants
Rate law expression
Rate= k [A]^m [B]^n
m and n are reaction orders
K is the arhenious constant or rate constant
If the concentration of a is doubled and the rate doubles
First order
If the concentration of a doubles and the rate quadruples
Second order
If the concentration of a triples and the rate triples
First order
If the concentration of a is triples and the the rate increases by a factor of 9
Second order
Straight line with a negative slope=
1st order
A first order reaction depends on
The concentration of one reactant raised to the first power
A second order reaction depends on the
Concentration of one reactant raised to the second power. Or, two reactants raised to the first power
Positive line
Second order
Collision model
The central idea that molecules must collide to react
Reactions depend on the energy and the orientation of the molecules
The kinetic molecular theory shows that higher temperatures result in more total collisions with greater energy
Activation energy
Minimum energy required to initiate a chemical reaction
When products have less energy than reactants
Exothermic reaction
Higher activation energy means
Slower reaction
Reaction mechanism
The steps by which a reaction occurs
Elementary reaction
Reaction that occurs in a single step
Molecularity of an elementary reaction
Number of molecules participating as reactants
Unimolecular
A yields products
Bimolecular
A +B yeilds products
Termolecular
A + B + C yeilds products (very unlikely)
Multi step mechanism
Reaction consisting of two or more elementary steps
Intermediate
A product of one elementary step that is consumed in another
Rate law of an elementary reaction is based directly on its
Molecularity (only true for elementary reactions)
Rate determining step
Slowest elementary step in a multistep mechanism
Kinetics
The study of how fast chemical reactions occur
