Chemistry Chemical Kinetics Flashcards
The ___ of a chemical reaction is the actual series of steps through which it occurs
mechanism
The slowest step in a proposed mechanism is called the rate-determining step, because the overall ___ cannot proceed faster than that step
reaction
___ is the study of the rates (or speed) of reactions
chemical kinetics
The ___ is the change of concentration of reactant or finished product with respect to time
reaction rate
Reactants -> Products
This equation indicates that ___ molecules are being consumed (concentration decreases) and the product molecules are being formed (concentration increases)
reactant
The process of chemical kinetics is concerned with how “fast” the ___ are being transformed into products
reactants
rate = decrease in concentration of ___/time = increase in concentration of products/time
reactants
Because the ___ of a reactant decreases during the reaction, a minus sign is placed before a rate that is expressed in terms of reactants
concentration
For the reaction 2A + B yields C:
The rate of reaction with respect to A is -(delta[A]/delta t)
with respect to B is -(delta[B]/delta t),
and with respect to C is (delta[C]/delta t)
___ is expressed in the units of moles per liter per second (mol/[Lxs) or molarity per second (molarity/s)
rate
rate = k[A]^x[B]^y
This expression is the ___ for the general reaction above, where k is the rate constant
rate law
The ___ is defined as a constant of proportionality between the chemical reaction rate and the concentration of the reactants
rate constant
The ___ x and y are called the orders of reaction; x is the order with respect to A, and y is the order with respect to B
exponents
It is important to note that the ___ of the rate law are not necessarily equal to the stoichiometric coefficients in the overall reaction equation
exponents
The exponents are equal to the ___ coefficients of the rate-determining step
stoichiometric
The overall order of a ___ (or the reaction order) is defined as the sum of the exponents, here equal to x + y
reaction
A zero-order reaction has a constant rate, which is independent of the ___ concentrations
reactants
A first-order ___ has a rate proportional to the concentration of one reactant.
rate = k[A] or rate = k[B]
reaction
A second-order reaction has a rate proportional to the ___ of the concentration of two reactants or to the square of the concentration of a single reactant
product
The ___ states that the rate of a reaction is proportional to the number of collisions per second
collision theory of chemical kinetics
It is important to note that ___ almost always increase with increasing temperatures. On the other hand, reaction rates decrease with decreasing temperatures
reaction rates
An ___ (one that leads to the formation of products) occurs only if the molecules collide with the correct orientation and sufficient force to break the existing bonds and form new ones
effective collision
The minimum energy of collision necessary for a reaction to take place is called the ___ E sub a, or the energy barrier
activation energy
Only a fraction of colliding ___ have enough kinetic energy to exceed the activation energy. This means that only a fraction of all collisions are effective
particles
When molecules collide with sufficient energy and in the correct orientation, they form a ___ in which the old bonds are weakened and the new bonds are beginning to form
transition state
The ___, also called the activated complex, has greater energy than either the reactants or the products and is denoted by a symbol
transition state
The activation energy is required to bring the reactants to this particular ___ level
energy
Once an activation complex is formed, it can either dissociate into the ___ or revert to reactants without any additional energy input
products
___ are distinguished from intermediates in that, existing as they do at energy maxima, transition states do not have a finite lifetime
transition states
A ___ illustrates the relationship between the activation energy, the heats of reaction, and the potential energy of the system before and after the reaction. The most important factors in such diagrams are the relative energies of the products and reactants. The enthalpy change of the reaction (delta H) is the difference between the potential energy of the products and the potential energy of the reactants. A negative enthalpy change indicates an exothermic reaction (where heat is given off), and a positive enthalpy change indicates an endothermic reaction (where heat is absorbed)
potential energy diagram
The ___ exists at the top of the energy barrier
activated complex
The difference in ___ between the activated complex and the reactants is the activation energy of the forward reaction; the difference in potential energies between the activated complex and the products is the activation energy of the reverse reaction
potential energies
Consequently, the proportion of ___ having energies greater than E sub a (and thus capable of undergoing reaction) increases with higher temperature
molecules
Therefore, the presence of a ___ causes the reaction to proceed more quickly toward equilibrium
catalyst
